Add a PR-Template

[Andre601]

I think it would be a good idea to have a Pull Request-template to always keep a consistent way of telling what was changed.

I had the following idea for a template:

[Pull Request]: https://github.com/botblock/discord-botlist-best-practices/pulls

## Please read
Before making a Pull Request, please make sure you've first checked that there is no open Pull Request with your change.

- [ ] I confirm that I checked the [Pull Request] page for any open PRs with similar changes.

## Changes
Please list your changes here in the corresponding category.

### Additions
- Added something

### Removals
- Removed something

### Changes
- Changed *this* to *that*

[renhiyama]

Just wastes more time writing 3x than just a small single line pull request honestly, but I agree with that confirmation thing only, also GitHub already shows what's changed in a pr, use that feature?