Document that pip supports Python 3.9
@@ -206,7 +206,7 @@ Upgrading pip
Python and OS Compatibility
===========================
-pip works with CPython versions 3.6, 3.7, 3.8 and also PyPy.
+pip works with CPython versions 3.6, 3.7, 3.8, 3.9 and also PyPy.
This means pip works on the latest patch version of each of these minor
versions. Previous patch versions are supported on a best effort approach.
