Allow for searching for PRs that need schema changes

Author: karenetheridge

.github/pull_request_template.md

@@ -14,7 +14,7 @@ present on the main branch, only on the development branches).
 Note that we do not accept changes to published specifications.
 -->
 
-<!-- Tick one of the following options: -->
+<!-- Tick one of the following options and remove the other two: -->
 
 - [ ] schema changes are included in this pull request
 - [ ] schema changes are needed for this pull request but not done yet