Add ref issue when creating pull request from issue

options/locale/locale_en-US.ini

@@ -1627,6 +1627,7 @@ issues.maybefixed = May be fixed by %s
 issues.create_branch_from_issue_success = Create branch %s from issue successfully
 issues.pr.completed = Completed
 issues.pr.conflicted = Merge conflicts
+issues.pr.not_exist_issue = Reference issue does not exist.
 issues.branch.latest = Latest commit %s
 issues.link.created = Created %s
 issues.num_participants = %d Participants