PR template

[otbutz]

Given the recent influx of AI slop hitting the repository, I'd recommend putting a PR template in place that includes a checkbox for having read and complied with the contributors guide: https://github.com/osm-search/Nominatim/blob/master/CONTRIBUTING.md

This won't magically get rid of AI slop, but at least adds two benefits:

• completely sidestepping the PR template serves as a potential red flag
• we can ban first-time offenders outright if they lied to us by checking the box

[lonvia]

Sounds like a good plan. Do you feel like making a proposal?

[otbutz]

#3934