Allow templates for pull requests

**Is your feature request related to a problem? Please describe.**
No

**Describe the solution you'd like**
GitHub allows you to add templates for PR descriptions. The templates are basically markdown pre-copy-pasted into the description field.

It works exactly as described here: https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/creating-a-pull-request-template-for-your-repository

**Describe alternatives you've considered**
You can enforce guidelines for pull requests on an external page...

But I am using a template right now to write this request. So I believe the utility should be self-evident.

**Additional context**