Update pull_request_template.md

Adding a task on contributors to add labels so PR reviewers will get notified to review

Author: narendasan

.github/pull_request_template.md

@@ -20,4 +20,5 @@ Please delete options that are not relevant and/or add your own.
 - [ ] I have commented my code, particularly in hard-to-understand areas and hacks
 - [ ] I have made corresponding changes to the documentation
 - [ ] I have added tests to verify my fix or my feature
-- [ ] New and existing unit tests pass locally with my changes
+- [ ] New and existing unit tests pass locally with my changes
+- [ ] I have added the relevant labels to my PR in so that relevant reviewers are notified