How can I add favicon asset? #1458

(Using v13.2.5)

I'd like to set the favicon on my documentation. I see that I can do this with --favicon myFavIcon.png since 5b66910
This does add the reference into index.html. But, I don't see how to add the favicon file itself into the generated assets. So, no favicon is found at runtime.
How do I add the icon? Am I just missing something obvious?