Add "[DO NOT MERGE]" to the list of WIP keywords.

Author: kennytm

homu/main.py

@@ -488,11 +488,20 @@ def parse_commands(body, username, repo_cfg, state, my_username, db, states,
                 continue
 
             # Ignore WIP PRs
-            if any(map(state.title.startswith, [
-                'WIP', 'TODO', '[WIP]', '[TODO]',
-            ])):
-                if realtime:
-                    state.add_comment(':clipboard: Looks like this PR is still in progress, ignoring approval')  # noqa
+            is_wip = False
+            for wip_kw in ['WIP', 'TODO', '[WIP]', '[TODO]', '[DO NOT MERGE]']:
+                if state.title.upper().startswith(wip_kw):
+                    if realtime:
+                        state.add_comment((
+                            ':clipboard:'
+                            ' Looks like this PR is still in progress,'
+                            ' ignoring approval.\n\n'
+                            'Hint: Remove **{}** from this PR\'s title when'
+                            ' it is ready for review.'
+                        ).format(wip_kw))
+                    is_wip = True
+                    break
+            if is_wip:
                 continue
 
             # Sometimes, GitHub sends the head SHA of a PR as 0000000