Here is a more detailed answer:
are we still talking about 'fork' with the github meaning rather than traditional meaning?
ngit will look for a nostr repo event  with the same 'earliest-unique-commit' as the first commit in the current git repo and post to that by default.
If it cant find any nostr repo events will ask for a naddr, which you can find on gitworkshop.dev.
If you commit the 'maintainers.yaml' file that gets created during `ngit init` it will post to the repo events it will ignore repo events from npubs not specified. This is a way of protecting against SPAM or scammers trying to claim your repo.