Add recommendation to choose squash commit message before merging

doc/development/code_review.md

@@ -432,6 +432,10 @@ When in doubt, ask someone from `@gitlab-com/gl-security/appsec` to review the m
     enough to `master`.
 - When you set the MR to "Merge When Pipeline Succeeds", you should take over
   subsequent revisions for anything that would be spotted after that.
+- For merge requests that have had [Squash and
+  merge](../user/project/merge_requests/squash_and_merge.md#squash-and-merge) set,
+  the squashed commit’s default commit message is taken from the merge request title.
+  You're encouraged to [select a commit with a more informative commit message](../user/project/merge_requests/squash_and_merge.md#overview) before merging.
 
 Thanks to **Pipeline for Merged Results**, authors no longer have to rebase their
 branch as frequently anymore (only when there are conflicts) because the Merge