[contributing] Add checklist item for requesting a new remote repo

Author: woojiahao

.github/PULL_REQUEST_TEMPLATE/submit_exercise.md

@@ -21,6 +21,7 @@ assignees: woojiahao
 
 ## Checklist
 
+- [ ] If you require a new remote repository on the `Git-Mastery` organization, have you [created a request](https://github.com/git-mastery/exercises/issues/new?template=request_exercise_repository.md) for it?
 - [ ] Have you written unit tests using [`repo-smith`](https://github.com/git-mastery/repo-smith) to validate the exercise grading scheme?
 - [ ] Have you tested the download script using `test-download.sh`?
 - [ ] Have you verified that this exercise does not already exist or is not currently in review?