chore(github): add pull request template.

Author: jbmoelker

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,15 @@
+## Summary
+
+Proposed changes:
+
+* ..
+* ..
+
+Resolves # .
+
+## Checklist
+
+* [ ] The changes only affect or contain one module.
+* [ ] The changes are according to [contribution guidelines](/CONTRIBUTING.md).
+* [ ] The new module is linked in the [list of available modules](/README.md#modules) (only if changes introduce new module).
+* [ ] The changes can be merged into the target branch without conflicts.