(DOCSP-26279): macOS emulator install instructions (#2335)

## Pull Request Info

add extra step for using Flutter SDK w macOS emulator

### Jira

- https://jira.mongodb.org/browse/DOCSP-26279

### Staged Changes

- [Install
(Flutter)](https://docs-mongodbcom-staging.corp.mongodb.com/realm/docsworker-xlarge/DOCSP-26279/sdk/flutter/install)

### Reminder Checklist

If your PR modifies the docs, you might need to also update some
corresponding
pages. Check if completed or N/A.

- [x] Create Jira ticket for corresponding docs-app-services update(s),
if any
- [x] Checked/updated Admin API
- [x] Checked/updated CLI reference

### Review Guidelines


[REVIEWING.md](https://github.com/mongodb/docs-realm/blob/master/REVIEWING.md)

source/sdk/flutter/install.txt

@@ -72,6 +72,32 @@ your Flutter project.
 
         import 'package:realm/realm.dart';
 
+.. _flutter-macos-development:
+
+Use Realm with the macOS App Sandbox
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you are developing with the Realm Flutter SDK in the macOS App Sandbox,
+network requests do not work by default due to built-in macOS security settings.
+Network access is required to use Atlas App Services and Device Sync.
+
+To enable network requests, add the following code to **both** the files
+:file:`macos/Runner/DebugProfile.entitlements` and :file:`macos/Runner/Release.entitlements`:
+
+.. code-block:: xml
+    :emphasize-lines: 2-3
+
+    <!--  Other entitlements -->
+    <key>com.apple.security.network.client</key>
+    <true/>
+    <!--  Other entitlements -->
+
+You can still use Realm Database locally without adding this network access permission.
+
+For more information about Flutter development for macOS, refer to `Building macOS apps with Flutter
+<https://docs.flutter.dev/development/platform-integration/macos/building#setting-up-entitlements>`__
+in the Flutter documentation.
+
 .. _dart-install-steps:
 
 Dart Standalone Installation