Create pull_request_template.md (#9)

detailed checklist will be added later

.github/pull_request_template.md

@@ -0,0 +1,13 @@
+## Summary
+<!--- This is a required section; please describe the main purpose of this proposed code change. --->
+
+<!---
+## Details
+This is an optional section; is there anything specific that reviewers should be aware of?
+--->
+
+## Testing Done
+<!--- This is a required section; please describe how this change was tested. --->
+
+Complete the following tasks before sending your PR, and replace `[ ]` with
+`[x]` to indicate you have done them.