Quote extras to guard shells with glob qualifiers

* Shells like zsh have glob qualifiers that will error if an extra
  is not quoted. While the glob qualifiers can be disabled, adding
  quotes guards against errors if people are copy-pasting or do not
  know that they can disable the behavior.

docs/html/cli/pip_install.rst

@@ -386,21 +386,21 @@ Examples
 
  .. code-block:: shell
 
- python -m pip install SomePackage[PDF]
+ python -m pip install "SomePackage[PDF]"
  python -m pip install "SomePackage[PDF] @ git+https://git.repo/SomePackage@main#subdirectory=subdir_path"
- python -m pip install .[PDF] # project in current directory
- python -m pip install SomePackage[PDF]==3.0
- python -m pip install SomePackage[PDF,EPUB] # multiple extras
+ python -m pip install ".[PDF]" # project in current directory
+ python -m pip install "SomePackage[PDF]==3.0"
+ python -m pip install "SomePackage[PDF,EPUB]" # multiple extras
 
  .. tab:: Windows
 
  .. code-block:: shell
 
- py -m pip install SomePackage[PDF]
+ py -m pip install "SomePackage[PDF]"
  py -m pip install "SomePackage[PDF] @ git+https://git.repo/SomePackage@main#subdirectory=subdir_path"
- py -m pip install .[PDF] # project in current directory
- py -m pip install SomePackage[PDF]==3.0
- py -m pip install SomePackage[PDF,EPUB] # multiple extras
+ py -m pip install ".[PDF]" # project in current directory
+ py -m pip install "SomePackage[PDF]==3.0"
+ py -m pip install "SomePackage[PDF,EPUB]" # multiple extras
 
 #. Install a particular source archive file.