Improve documentation on pygit2 versions (#32779)
Improve documentation on pygit2 versions (#32779)

This adds an explanation of the python-cffi dep added in pygit2 0.21.0,
and recommends 0.20.3 for LTS distros. It also links to the salt-pack
issue which tracks the progress of adding pygit2 to our Debian and
Ubuntu repositories.
saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt