Add a pull request template (#272)

Author: TiejunMS

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,5 @@
+## PR checklist
+<!--- Put an `x` in all the boxes that apply. -->
+- [ ] Updated function header with a short description and version number
+- [ ] Added test case for bug fix or new feature
+- [ ] Validated on real hardware <!-- hardware - toolchain -->