I’ve googled and found nothing. I feel like there must be an incredibly obvious answer that I am missing because I would imagine that other folks have wanted to to do the same? The use case is so that the iOS bookmark on my home screen looks nice. 
Believe it or not, this hasn’t come up before, and there is no way to do this without editing the code after you install it. Just to clarify, you are seeing the standard HADasboard icon. like this:
Right?
Ha, I am sincerely shocked. Yes, that is the icon I am seeing.
I’ll add custom favicons to my list of hings to do
Awesome. Just installed yesterday, and today came looking for this. Nice to know it’s on the list.