Update Pull Request Template

[kilianvolmer]

Description

The template for pull requests is now outdated. The links need to be updated to readthedocs and the check for documentation needs to be rewritten.

Version

Any

To reproduce

Open a pull request

Relevant log output

Add any relevant information, e.g. used compiler, screenshots.

Checklist

• [x] Attached labels, especially loc:: or model:: labels.
• [x] Linked to project