chore: add config / docs for 'pre-commit' support (#103)

Source-Author: Tres Seaver <tseaver@palladion.com>
Source-Date: Tue Dec 1 16:01:20 2020 -0500
Source-Repo: googleapis/synthtool
Source-Sha: 32af6da519a6b042e3da62008e2a75e991efb6b4
Source-Link: https://github.com/googleapis/synthtool/commit/32af6da519a6b042e3da62008e2a75e991efb6b4
3 files changed