Document not requiring r-b/a-b tags in commit messages.

Since we have marge, you get a link back to the discussion acking a
merge.

Part-of: <!25>
3 jobs for master in 3 minutes and 7 seconds (queued for 1 second)
Status Name Job ID Coverage
  Container
passed alpine-image #8194437

00:00:11

 
  Test
passed check-file-uniqueness #8194438
packet.net

00:00:36

 
  Deploy
passed upload-to-minio #8194439
packet.net

00:02:19