add a pull request template

Summary: To encourage more detail in PRs

Reviewed By: rchen152

Differential Revision: D87606058

fbshipit-source-id: c8046683280db2149cd70e22deb55ca88bd1704f

Author: yangdanny97

.github/pull_request_template.md

@@ -0,0 +1,11 @@
+# Summary
+
+<!-- Describe the change in this PR -->
+
+Fixes #XXXX
+
+# Test Plan
+
+<!-- Describe how you tested this PR -->
+
+<!-- Run test.py and commit any changes to generated files -->