Update pull_request_template.md

Author: rmorshea

.github/pull_request_template.md

@@ -1,7 +1,12 @@
-## Checklist
+## Issues
+
+<!-- Link the issues this change resolves, or describe them -->
+
+## Summary
 
-Please update this checklist as you complete each item:
+<!-- Describe how these changes resolve the aforementioned issues -->
+
+## Checklist
 
 - [ ] Tests have been included for all bug fixes or added functionality.
 - [ ] The `changelog.rst` has been updated with any significant changes.
-- [ ] GitHub Issues which may be closed by this Pull Request have been linked.