added a minimal PR template

.github/pull_request_template.md

@@ -0,0 +1,19 @@
+<!--
+Do NOT open a PR without discussing the changes on an open issue, first.
+
+Add the issue number here. e.g. #123
+-->
+fixes #
+
+<!-- formalities. These are not optional. -->
+
+- [ ] I have read the [Contribution Guidelines](../CONTRIBUTING.md)
+- [ ] I have commented on the issue above and discussed the intended changes
+- [ ] A maintainer has signed off on the changes and the issue was assigned to me
+- [ ] All newly added code is adequately covered by tests
+- [ ] All existing tests are still running without errors
+- [ ] The documentation was modified to reflect the changes _OR_ no documentation changes are required.
+
+## Changes
+
+<!-- describe the changes you made. -->