This is something that you can do by providing a `preferred-citation` in a CITATION.cff file. This will be rendered on GitHub as the thing to cite. See the schema guide section about this here: https://github.com/citation-file-format/citation-file-format....
Ah, interesting. Thanks! I was experimenting with the "references" key to see if it can do what I want and somehow missed that "preferred-citation" exists. Was this added after the initial GitHub announcement?