PULL_REQUEST_TEMPLATE

## Purpose
- Clear, easy-to-understand sentences outlining the purpose of the PR
## Proposed Changes
- [ADD] ...
- [CHANGE] ...
- [REMOVE] ...
- [FIX] ...
## Issues
- Links to relevant issues
- Example: issue-XYZ
## Testing
- Provide some proof you've tested your changes 
- Example: test results available at ...
- Example: tested on operating system ...