feat(github): add pull request template (#830)

* feat(github): add pull request template

* feat(github): rephrase pr template

Author: DexterYan

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,21 @@
+## Description, Motivation and Context
+
+Please include a summary of the change or what problem does it solve. Please also include relevant motivation and context.
+
+<!--- If it relates to an open issue, please link to the issue here.
+e.g.
+Fixes: #414
+-->
+
+## Checklist
+
+- [ ] New and existing tests pass locally with the changes.
+- [ ] Tests for the changes have been added (for bug fixes / features)
+- [ ] The commit message(s) are informative and highlight any breaking changes
+
+## Does this PR introduce a breaking change?
+- [ ] Yes
+- [ ] No
+
+<!-- If this PR contains a breaking change, please describe the impact and migration path for existing applications below. -->
+