Update install instructions to work with zsh default Mac shell (#2258)

README.md

@@ -40,9 +40,9 @@ in order to install VisPy (one of the packages we depend on) on Windows machines
 The simplest command to install with pip is:
 
 ```sh
-pip install napari[all]
+pip install 'napari[all]'
 ```
- 
+
 (See `Specifying a GUI Backend` below for an explanation of the `[all]` notation.)
 Note: while not strictly required, it is *highly* recommended to install
 napari into a clean virtual environment using an environment manager like
@@ -52,7 +52,7 @@ napari into a clean virtual environment using an environment manager like
 ```sh
 conda create -y -n napari-env python=3.8
 conda activate napari-env
-pip install napari[all]
+pip install 'napari[all]'
 ```
 
 ### from source
@@ -62,7 +62,7 @@ To clone the repository locally and install in editable mode use
 ```sh
 git clone https://github.com/napari/napari.git
 cd napari
-pip install -e .[all]
+pip install -e '.[all]'
 
 # or, to install in editable mode AND grab all of the developer tools
 # (this is required if you want to contribute code back to napari)
@@ -83,16 +83,16 @@ For more information or troubleshooting see our [installation tutorial](https://
 > running napari will result in an error message asking you to install one of
 > them.
 >
-> Running `pip install napari[all]` will install the default framework – currently
+> Running `pip install 'napari[all]'` will install the default framework – currently
 > PyQt5, but this could change in the future.
 >
 > To install napari with a specific framework, you can use:
 >
 > ```sh
-> pip install napari[pyqt5]    # for PyQt5
+> pip install 'napari[pyqt5]'    # for PyQt5
 >
 > # OR
-> pip install napari[pyside2]  # for PySide2
+> pip install 'napari[pyside2]'  # for PySide2
 > ```
 
 ## simple example

docs/index.md

@@ -15,7 +15,7 @@ napari can be installed on most macOS, Linux, and Windows systems with
 Python 3.7 and 3.8 using pip:
 
 ```sh
-pip install napari[all]
+pip install 'napari[all]'
 ```
 
 napari needs a library called [Qt](https://www.qt.io/) to run its user
@@ -31,11 +31,11 @@ them.
 To install napari with a specific UI framework, you can use
 
 ```sh
-pip install napari[pyqt5]
+pip install 'napari[pyqt5]'
 # or
-pip install napari[pyside2]
+pip install 'napari[pyside2]'
 # or
-pip install napari[all]
+pip install 'napari[all]'
 ```
 
 This last option (`pip install napari[all]`) will choose a framework for