Updates the PR template. (#1494)

* The old PR template was annoying.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,18 +1,12 @@
 ## Description
-
-The what and why - include a summary of the change, describe what it does, and include relevant motivation and context.
-
-Fixes _JIRA/GitHub issue number_
+<!-- *(mandatory)* Detail your pull request, with the what, why and how. -->
 
 ## Engineering checklist
-*Check only items that apply*
+<!-- *Check only items that apply* -->
 
 - [ ] Documentation updated
 - [ ] Covered by unit tests
 - [ ] Covered by integration tests
 
 ## Test instructions
 <!-- *(optional)* Describe any non-standard test instructions and configuration settings. Delete this section if not applicable. -->
-
-## Notes for code reviewers
-<!-- *(optional)* Mention any relevant information for code reviewers. Delete this section if not applicable. -->