docs: add PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,16 @@
+## Changes
+
+- This PR... (please explain what changes you made and why).
+- Fixes #issue_number (if the PR fixes an open issue)
+
+## Testing
+
+<!--
+How can the reviewers verify this change? What tests did you add to verify your changes?
+-->
+
+## Additional Information
+
+<!--
+Any additional information that you think is important and relevant to this pull request.
+-->