Add additional context to `protected_pip.py` about how it works
Add additional context to `protected_pip.py` about how it works

This should make it easier to understand what this file is doing,
and when it is useful.

pradyunsg/pip,pypa/pip,pradyunsg/pip,pypa/pip,pfmoore/pip,pfmoore/pip,sbidoul/pip,sbidoul/pip