Update src/pip/_vendor/README.rst
Update src/pip/_vendor/README.rst

Co-authored-by: Pradyun Gedam <d57123e724a720d5727375fe7954e02b18dae45d@gmail.com>
pradyunsg/pip,pypa/pip,sbidoul/pip,pfmoore/pip,sbidoul/pip,pypa/pip,pradyunsg/pip,pfmoore/pip