Github links to wrong(?) contributing doc when opening first PR

This one might be tricky to recreate... on opening my first PR, github suggested I read the contributing guidelines for this repo, and linked to https://github.com/getodk/docs/blob/d573ca180665f59207e1728d39ad00c9e1172b81/docs/contributing.rst, which does not contain any information.

Start by opening docs/contributing.rst at commit d573ca180665f59207e1728d39ad00c9e1172b81 and compare it with the repository's current contributing guidance. Investigate why GitHub's first-PR prompt resolves to that historical file, and consider the issue complete when the prompt links to the intended document containing contribution information.

Written by the indexing model from the issue text.