Add a mention of the merge request into its default commit message.

CHANGELOG

@@ -7,6 +7,7 @@ v 7.1.0
   - Add @all mention for comments
   - Dont show reply button if user is not signed in
   - Expose more information for issues with webhook
+  - Add a mention of the merge request into the default merge request commit message
 
 v 7.0.0
   - The CPU no longer overheats when you hold down the spacebar

app/models/merge_request.rb

@@ -293,6 +293,8 @@ class MergeRequest < ActiveRecord::Base
     message << title.to_s
     message << "\n\n"
     message << description.to_s
+    message << "\n\n"
+    message << "See merge request !#{iid}"
     message
   end