Improve PR template

To ensure any PR makes:
- update in changelog
- add or update test to cover the new changes
- update documentations

Author: ahangarha

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,17 +1,18 @@
 ### Summary
 
-Provide a general description of the code changes in your pull
+_Remove this paragraph and provide a general description of the code changes in your pull
 request... were there any bugs you had fixed? If so, mention them. If
 these bugs have open GitHub issues, be sure to tag them here as well,
-to keep the conversation linked together.
+to keep the conversation linked together._
 
 ### Other Information
 
-If there's anything else that's important and relevant to your pull
-request, mention that information here. This could include
-benchmarks, or other information.
+_Remove this parapraph and mention any other important and relevant information such as benchmarks._
 
-If you are updating any of the CHANGELOG files or are asked to update the
-CHANGELOG files by reviewers, please add the CHANGELOG entry at the top of the file.
+### Pull Request checklist
+_Remove this line after checking all the items here. If the item is not applicable to the PR, both check it out and wrap it by `~`._
 
-Thanks for contributing!
+- [ ] Add/update test to cover these changes
+- [ ] Update documentation
+- [ ] Update CHANGELOG file  
+  _Add the CHANGELOG entry at the top of the file._