Create a pull request template

[raccube]

We need a pull request template which prompts the user to test their change and asks which platforms the change was tested on.

[trickeydan]

## Platforms Affected

- [ ] ODROID U3
- [ ] Raspberry Pi 3/3B+
- [ ] Raspberry Pi 4

## Checklist

- [ ] I have updated the relevant documentation
- [ ] I have tested builds of my changes on all affected platforms
- [ ] I would like multiple reviewers to approve my code before merging

## Why do you want to make these changes?


## Which parts of the build process do your changes affect?


## Do your changes affect student or volunteer experience? How so?


## Are your changes related to any existing issues or PRs? How so?

[raccube]

Shouldn't the first section be called Tested Platforms instead?

[raccube]

Although whoever is reviewing should test it themselves as well