[docs] Add "Getting Started" docs (#8934)

Context: 5915027

I forgot to add `Documentation/docs-mobile/getting-started` as part
of commit 5915027!

Oops.

Add the overlooked documentation.

Documentation/docs-mobile/getting-started/installation/dependencies.md

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+---
+title: "Install .NET for Android dependencies"
+description: "Learn how to install .NET for Android dependencies so you can create native Android applications."
+ms.date: 11/01/2023
+---
+# Install .NET for Android dependencies
+
+In order to build .NET for Android applications you need to install the Android SDK and the Java SDK.
+
+## Using "InstallAndroidDependencies" target
+
+The easiest way to install the required dependencies for your Android application is to run the
+[`InstallAndroidDependencies`](../../building-apps/build-targets.md#installandroiddependencies)
+MSBuild target.
+
+This target will examine your application project and install the exact components which are needed.
+If you update your project to target a new Android API you will need to run this target again
+to make sure you get the required components.
+
+For example if you are upgrading your project to target API 34 from API 32, you will only have
+API 32 installed. Running the `InstallAndroidDependencies` target will install API 34 for you.
+
+If you do not have the Android SDK installed at all, this target can also handle installing the SDK
+on a clean machine. You can change the destination of the installation by setting the
+`AndroidSdkDirectory` MSBuild property.  It will also install the Java SDK if the `JavaSdkDirectory`
+MSBuild property is provided.
+
+```dotnetcli
+dotnet build -t:InstallAndroidDependencies -f net8.0-android -p:AndroidSdkDirectory=c:\work\android-sdk -p:JavaSdkDirectory=c:\work\jdk -p:AcceptAndroidSdkLicenses=True
+```
+
+Here are all the arguments which the target will use when installing the dependencies:
+
+* `-p:AndroidSdkDirectory="<PATH>"` installs or updates Android dependencies to the specified path.  
+    *Note*: You must use an absolute path; Unix developers should not use tilde (`~`), as it is
+    not expanded when used *within* a command-line argument.
+
+* `-p:JavaSdkDirectory="<PATH>"` installs Java to the specified path.  
+    *Note*: You must use an absolute path; Unix developers should not use tilde (`~`), as it is
+    not expanded when used *within* a command-line argument.
+
+* `-p:AcceptAndroidSDKLicenses=True` accepts the necessary Android licenses for development.
+
+> [!NOTE]
+> To make development easier try to avoid using paths which contain spaces or non-ASCII characters.
+
+## Install the Android SDK manually
+
+You might find it necessary to install the Android SDK manually:
+
+ 1. Go to [Android Studio download](https://developer.android.com/studio#download).  
+    Scroll down to the "Command Line Tools only" section and download the zip file for your operating system.
+
+ 2. Create an `android-sdk` directory somewhere on your hard drive. To make your life easier create it near to the root of the drive. For example `c:\android-sdk`.
+
+ 3. Extract the files from the zip file into this directory. You should end up with a folder structure like
+  `android-sdk\cmdline-tools`
+
+ 4. Open a terminal or Command Prompt.
+
+ 5. Navigate to the `android-sdk\cmdline-tools\bin` directory within the directory you created.
+
+ 6. Run the `sdkmanager` command to install the desired components.
+
+For example, to install the latest platform and platform tools, use:
+
+```console
+sdkmanager "platforms;android-34" "platform-tools" "build-tools;34.0.0" "emulator" "system-images;android-34;default;x86_64" "cmdline-tools;11.0" --sdk_root=c:\android-sdk
+```
+
+Note that double-quotes should be used liberally to enclose the semicolon `;`, which is part of the component names.
+
+You will be prompted to accept the license, after which the Android SDK will install.
+
+You can use `sdkmanager` to install additional components. You can use the `--list` argument to get a list of all the available components. You can then look through the list and find the additional components you want.
+
+```console
+sdkmanager --list
+```
+
+The following component types are useful to know:
+
+  * `platforms;android-XX`: Installs the platform `android-XX` into the sdk.
+    Replace *XX* with the API Level of your chosen platform.
+    For example `platforms;android-30` will install Android API 30, while
+    `platforms;android-21` will install Android API 21.
+
+  * `system-images;android-XX;default;x86_64`: Installs an emulator image for
+    the specific API level. The `x86_64` can be swapped out for different ABIs
+    such as `x86`, `arm64-v8a`, and `x86_64`. These reflect the ABI of the image
+    being installed. This can be useful if you have issues on specific ABI's.
+
+It is also good practice to set the `ANDROID_HOME` environment variable, as this
+allows you to use certain tooling from the command line.
+
+## Install Microsoft JDK manually
+
+In order to build .NET for Android applications or libraries you need to have a version of the Java Development Kit installed.
+We recommend you use the Microsoft Open JDK, this has been tested against our .NET for Android builds:
+
+ 1. Download [Microsoft OpenJDK 11](/java/openjdk/download#openjdk-11).
+
+ 2. Depending on your platform run the appropriate installer.
+
+ 3. It is also good practice to set the `JAVA_HOME` environment variable.
+    This will allow you to use the JDK from the Command Prompt or Terminal.

Documentation/docs-mobile/getting-started/installation/index.md

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+---
+title: Installation
+description: Install .NET for Android
+ms.date: 04/17/2024
+---
+
+# Installation overview
+
+.NET for Android allows writing applications for the
+[Android Operating System](https://developer.android.com) using .NET.
+
+In order to use .NET for Android, you must first
+[install .NET for Android](net-android.md), and then you need to
+[install dependencies such as the Android SDK](dependencies.md).

Documentation/docs-mobile/getting-started/installation/net-android.md

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+---
+title: "Install .NET for Android"
+description: "Learn how to install .NET for Android so you can create native android applications."
+ms.date: 11/01/2023
+---
+# Install .NET for Android
+
+Developing native, .NET for Android apps requires .NET 6 or higher. Various IDE's can be used, however
+we recommend Visual Studio 2022 17.3 or greater, or Visual Studio Code.
+
+<!-- markdownlint-disable MD025 -->
+## [Install via the Command Prompt or Terminal](#tab/commandline)
+<!-- markdownlint-enable MD025 -->
+
+ 1. Install the [latest .NET](https://dotnet.microsoft.com/download) for your particular platform
+    and follow its [installation instructions](/dotnet/core/install).
+
+ 2. From a Command Prompt or Terminal run:
+
+    ```dotnetcli
+    dotnet workload install android
+    ```
+
+ 3. In order to build Android applications you also need to install the
+    [Android SDK and other dependencies](dependencies.md#using-installandroiddependencies-target).
+
+
+<!-- markdownlint-disable MD025 -->
+## [Install via Visual Studio](#tab/visualstudio)
+<!-- markdownlint-enable MD025 -->
+
+ 1. Install the [latest Visual Studio](https://visualstudio.microsoft.com/downloads/).
+
+ 2. Select the .NET Multi Platform App UI Development workload and any other workloads you want.
+
+    ![Select .Net Multi Platform App UI WorkLoad](images/vs-install-select-maui.png)
+
+ 3. Or select the .NET for Android SDK component from the Individual Components tab.
+
+    ![Select .NET for Android SDK Component](images/vs-install-select-android-components.png)
+
+ 4. Let the installer run, it may take a while depending on your Internet Connection.
+
+    ![The Running Installer](images/vs-install-installing.png)
+
+ 5. Once installed you can run Visual Studio.
+
+    You will be presented with the start up screen. Select New Project:
+
+    ![Select the New Project Menu](images/vs-new-project.png)
+
+ 6. Look through the templates to find the Android Application Template
+
+    ![Select the Android Application Template](images/vs-select-android-application.png)

Documentation/docs-mobile/index.yml

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+### YamlMime:Hub
+
+#root section (Required)
+title: .NET for Android documentation
+summary: >
+  .NET for Android allows you to write Android apps using .NET languages.
+brand: dotnet
+
+metadata:
+  title: .NET for Android
+  description: The .NET for Android guide has everything you need to learn .NET on the Android platform.
+  ms.service: dotnet-android
+  ms.topic: hub-page
+  author: jonpryor
+  ms.author: jopryo
+  ms.date: 04/18/2024
+
+# highlightedContent section (Optional; Remove if not applicable.)
+# Maximum of 8 items
+highlightedContent:
+# itemType: architecture | concept | deploy | download | get-started | how-to-guide | training | overview | quickstart | reference | sample | tutorial | video | whats-new
+  items:
+    # Card
+    - title: Install .NET for Android
+      itemType: get-started
+      url: ./getting-started/installation/index.md
+
+conceptualContent:
+# itemType: reference
+  # Supports up to 3 subsections
+  sections:
+    - title: .NET for Android reference
+      items:
+        # Card
+        - title: Building Android Apps
+          summary: Building Android Apps
+          links:
+            - url: ./building-apps/build-process.md
+              itemType: reference
+              text: Build Process
+            - url: ./building-apps/build-targets.md
+              itemType: reference
+              text: Build Targets
+            - url: ./building-apps/build-properties.md
+              itemType: reference
+              text: Build Properties
+            - url: ./building-apps/build-items.md
+              itemType: reference
+              text: Build Items
+        # Card
+        - title: Features
+          summary: .NET for Android Features
+          links:
+            - url: ./features/layout-code-behind/index.md
+              itemType: reference
+              text: Layout Code Behind
+            - url: ./features/maven/android-maven-library.md
+              itemType: reference
+              text: "@(AndroidMavenLibrary) Build Item"
+        # Card
+        - title: Message reference
+          summary: Tooling error and warning message reference.
+          links:
+            - url: ./messages/index.md
+              itemType: reference
+              text: Messages reference
+
+
+# additionalContent section (Optional; Remove if not applicable.)
+# Card with links style
+additionalContent:
+  # Supports up to 4 subsections
+  sections:
+
+    - title: API reference # < 60 chars (optional)
+      summary: Search the .NET API documentation. # < 160 chars (optional)
+      items:
+        # Card
+        - title: ".NET API reference"
+          summary: API reference documentation for .NET
+          url: /dotnet/api/index.md?view=net-8.0
+        # Card
+        - title: ".NET for Android reference"
+          summary: Android-specific API reference
+          url: /dotnet/api/?preserve-view=true&view=net-android-34.0
+
+  # footer (Optional; Remove if not applicable.)
+  footer: "Are you interested in contributing to the .NET docs? For more information, see our [contributor guide](/contribute/dotnet/dotnet-contribute)."