Add PR template

.github/pull_request_template.md

@@ -0,0 +1,23 @@
+<!--- Note to EXTERNAL Contributors -->
+<!-- Thanks for opening a PR!
+If it is a significant code change, please **make sure there is an open issue** for this.
+We work best with you when we have accepted the idea first before you code. -->
+
+<!--- For ALL Contributors 👇 -->
+
+## What was changed
+<!-- Describe what has changed in this PR -->
+
+## Why?
+<!-- Tell your future self why have you made these changes -->
+
+## Checklist
+<!--- add/delete as needed --->
+
+- Closes #<!-- add issue number here -->
+- How was this tested:
+  <!--- Please describe how you tested your changes/how we can test them -->
+  <!-- - Added autotests -->
+- Any docs updates needed?
+  <!--- Provide a part of the documentation that should be updated
+        or a link to related PR in the documentation repository -->