Addition of sensible default

Author: cmccarthy1

.github/pull_request_template.md

@@ -0,0 +1,5 @@
+Please go the the `Preview` tab and select the appropriate sub-template:
+
+* [Bug fix Pull Request](?expand=1&template=bug.md)
+* [Feature addition Pull Request](?expand=1&template=feature.md)
+* [Documentation addition Pull Request](?expand=1&template=documentation.md)