Added documentation

Author: pfmoore

docs/html/user_guide.rst

@@ -782,6 +782,49 @@ This is now covered in :doc:`../topics/repeatable-installs`.
 
 This is now covered in :doc:`../topics/dependency-resolution`.
 
+.. _`Managing a different Python interpreter`:
+
+Managing a different Python interpreter
+=======================================
+
+Occasionally, you may want to use pip to manage a Python installation other than
+the one pip is installed into. In this case, you can use the ``--python`` option
+to specify the interpreter you want to manage. This option can take one of three
+values:
+
+#. The path to a Python executable.
+#. The path to a virtual environment.
+#. Either "py" or "python", referring to the currently active Python interpreter.
+
+In all 3 cases, pip will run exactly as if it had been invoked from that Python
+environment.
+
+One example of where this might be useful is to manage a virtual environment
+that does not have pip installed.
+
+.. tab:: Unix/macOS
+
+   .. code-block:: console
+
+      $ python -m venv .venv --without-pip
+      $ python -m pip --python .venv install SomePackage
+      [...]
+      Successfully installed SomePackage
+
+.. tab:: Windows
+
+   .. code-block:: console
+
+      C:\> py -m venv .venv --without-pip
+      C:\> py -m pip --python .venv install SomePackage
+      [...]
+      Successfully installed SomePackage
+
+You could also use ``--python .venv/bin/python`` (or on Windows,
+``--python .venv\Scripts\python.exe``) if you wanted to be explicit, but the
+virtual environment name is shorter and works exactly the same.
+
+
 .. _`Using pip from your program`:
 
 Using pip from your program

news/11320.feature.rst

@@ -1 +1,2 @@
-Add a ``--python`` option to specify the Python environment to be managed by pip.
+Add a ``--python`` option to allow pip to manage Python environments other
+than the one pip is installed in.