Add "Overcommit: The Opinionated Git Hook Manager" article

Debut of our newly-minted `overcommit` gem for managing git hooks.

Change-Id: Iae6bd48d42281b57928a946c61585e5dd54beeea
Reviewed-on: https://gerrit.causes.com/23114
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Aaron Neyer <aaron.neyer@causes.com>