There's not much to it really. It's just an ed25519 key which has the same 64 byte hex string that nostr does for its privkey. So nostr already has an an ed25519 privkey which is native to git. It can do commits, ssh, clones, git identity etc. The #pubky is simply a base32 encoded public key in the profile (just like npub but better, without the unnecessary segwit checksum). So every nostr account gets both functionalities. Perfect for git.