We already redirect sources to repo if there's only one[1]. Why not also if
there's only one public?

As an example, I have a dotfiles[2] project with a public dotfiles repo and an unlisted
dotfiles-docs repo. I use the docs repo for the project's README (because I don't
want a README in my home dir). 

1: https://todo.sr.ht/~sircmpwn/hub.sr.ht/23
2: https://sr.ht/~adamski/dotfiles/