Update pr template with link to migration (#3459)

Add link to docs.

.github/pull_request_template.md

@@ -11,7 +11,7 @@ _Remove unnecessary checks_
 **Changes in Models:**
 - [ ] Did I update or add new fake data?
 - [ ] Did I squash my migration?
-- [ ] If my changes are not backward-compatible, did I schedule a deploy with the rest of the team?
+- [ ] [Are my changes backward-compatible](https://github.com/mozilla/foundation.mozilla.org/blob/master/docs/workflow.md#django-migrations-what-to-do-when-working-on-backward-incompatible-migrations). If not, did I schedule a deploy with the rest of the team?
 
 **Documentation:**
 - [ ] Is my code documented?