add PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,13 @@
+### Motivation
+
+*Replace this line with why you are making this change.*
+
+### Have you...
+
+  - [] Written a sample in `_samples`?
+  - [] Updated documentation in the `docs/` folder?
+  - [] Linked this PR to an issue?
+  - [] Written any automated tests?
+  - [] Refactored your code to be maintainable?
+
+The above things are not required, but appreciated.