Add PR template file (#3)

Signed-off-by: jinhai <haijin.chn@gmail.com>

.github/PULL_REQUEST_TEMPLATE.md

+**What type of PR is this?**
+
+- [ ] API-change
+- [ ] BUG
+- [ ] Improvement
+- [ ] Documentation
+- [ ] Feature
+- [ ] Test and CI
+- [ ] Code Refactoring
+
+**Which issue(s) this PR fixes:**
+
+Fixes #
+
+**What this PR does / why we need it:**
+
+Not Available
+
+**Special notes for your reviewer:**
+
+Not Available
+
+**Additional documentation (e.g. design docs, usage docs, etc.):**
+
+Not Available