comment when auto-flagging as admin review (bug 1109701)

Fixes [bug 1109701](https://bugzilla.mozilla.org/show_bug.cgi?id=1109701)

This is following [bug 540028](https://bugzilla.mozilla.org/show_bug.cgi?id=540028) (PR #139) and [bug 1097634](https://bugzilla.mozilla.org/show_bug.cgi?id=1097634) (PR #363):
automatically add a review comment saying that the version has been flagged as "admin review" because some sources were provided.