Co-maintainer wanted

Hi! I don't have any use for Tandem any more due to multiple reasons, and I also no longer have an account to log into Tandem with. As such, I can only test if Tandem actually launches when I update the Flatpak — I can't check if things beyond that work. Thus, it would be nice to have a co-maintainer of this package who uses it more.

With that said, I'm going to keep this updated regardless of whether someone steps up and ensure that new versions actually launch, but I can't do much more than that.