[issue40558] update CONTRIBUTING.rst docs

[Zachary Ware]

Zachary Ware <zachary.ware at gmail.com> added the comment:

The very tiny disk on buildbot.python.org had filled up; its had some space cleared and is now working again.

----------

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40558>
_______________________________________