Add link to source on overcommit article

There's a link in the document body, but it doesn't hurt to make it easy
to discover the source location.

Change-Id: I22b7e713f0551cceb0cfa722eb988f0716436d9f
Reviewed-on: https://gerrit.causes.com/23127
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>