Update PR Template (#364)

* PR template

* update previous template file

Author: e7mac

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,8 +1,14 @@
-Fixes #
+What              | Where/Who
+------------------|----------------------------------------
+JIRA Issue        | [JIRA_TICKET_ID](https://leanplum.atlassian.net/browse/JIRA_TICKET_ID)
+People Involved   | @colleague1, @colleague2
 
-## Proposed Changes
+[Notes on PR descriptions](https://leanplum.atlassian.net/wiki/spaces/PR/pages/288424408/Creating+a+GitHub+Pull+Request)
 
-  -
-  -
-  -
+## Background
 
+## Implementation
+
+## Testing steps
+
+## Is this change backwards-compatible?