Update PULL_REQUEST_TEMPLATE.md

Author: alexjpwalker

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,9 +1,7 @@
-Please replace every line in curly brackets { like this } with an appropriate description, and remove this line.
+## Usage and product changes
 
-## What is the goal of this PR?
 
-{ Please describe the goal of this PR, why they are valuable to achieve, and reference the related GitHub issues. }
+## Motivation
 
-## What are the changes implemented in this PR?
 
-{ Please explain what you implemented, why your changes are the best way to achieve the goal(s) above, and reference the GitHub issues to be automatically closed, such like 'closes #number'. }
+## Implementation