GitHub is alien to me lol, it's not like a add a relay tho is it(?)
Yes their is a bridge.
https://github.com/8go/matrix-nostr-bridge
It's one of the better more reliable privacy focused messengers out there, imo. Used it extensively for a few years now for family and friends. I akin it to a modern interpretation of XMPP protocol, it just works.
Discussion
No it's just a way of publishing a matrix message as a nostr note and vice versa.