add triage instructions to add all tickets to the same milestone

howto/git.md

@@ -316,6 +316,9 @@ gitolite.
 
 It assumes the repository has already been migrated.
 
+ 1. (optional) triage the ticket with the labels ~Git and ~Gitweb, and
+    the milestone %"legacy Git infrastructure retirement (TPA-RFC-36)"
+
  4. make an (executable) `pre-receive` hook in `git-rw` with an exit
     status of `1` warning about the new code location, this can be
     done with this Fabric command: