[Misc] Update PULL_REQUEST_TEMPLATE.md (#4710)

* Update PULL_REQUEST_TEMPLATE.md

* Update PULL_REQUEST_TEMPLATE.md

* Update PULL_REQUEST_TEMPLATE.md

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,11 +5,11 @@ It'll be great if relevant reviewers can be assigned as well.-->
 ## Checklist
 Please feel free to remove inapplicable items for your PR.
 - [ ] The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
-- [ ] Changes are complete (i.e. I finished coding on this PR)
+- [ ] I've leverage the [tools](https://docs.google.com/document/d/1iHyj7zlmygKSk5gBPsqIqL5ASPzJSPREaNT_QdsiYA4/edit) to beautify the python and c++ code.
+- [ ] The PR is complete and small, read the [Google eng practice (CL equals to PR)](https://google.github.io/eng-practices/review/developer/small-cls.html) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
 - [ ] All changes have test coverage
 - [ ] Code is well-documented
-- [ ] To the best of my knowledge, examples are either not affected by this change,
-      or have been fixed to be compatible with this change
+- [ ] To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
 - [ ] Related issue is referred in this PR
 - [ ] If the PR is for a new model/paper, I've updated the example index [here](../examples/README.md).