PULL_REQUEST_TEMPLATE.md

## What does this PR do?
Add resource(s) | Remove resource(s) | Add info | Improve repo

## For resources
### Description 

### Why is this valuable (or not)?

### How do we know it's really free?

### For book lists, is it a book? For course lists, is it a course? etc.

## Checklist:
- [ ] Read our [contributing guidelines](/CONTRIBUTING.md)
- [ ] Search for duplicates.
- [ ] Include author(s) and platform where appropriate.
- [ ] Put lists  in alphabetical order, correct spacing.
- [ ] Add needed indications (PDF, access notes, under construction)

## Followup

- Check the output of Travis-CI for linter errors!