Update docs to match behaviour

Author: pfmoore

docs/html/topics/python-option.md

@@ -5,14 +5,13 @@
 
 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
+to specify the interpreter you want to manage. This option can take one of two
 values:
 
 1. The path to a Python executable.
 2. The path to a virtual environment.
-3. 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
+In both 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