docs(python): document adding Python 3.9 support, dropping 3.5 support (#120) Closes #787 Source-Author: Tres Seaver <[email protected]> Source-Date: Thu Dec 17 16:08:02 2020 -0500 Source-Repo: googleapis/synthtool Source-Sha: b670a77a454f415d247907908e8ee7943e06d718 Source-Link: https://github.com/googleapis/synthtool/commit/b670a77a454f415d247907908e8ee7943e06d718