New review comment by ifreund on void-packages repository

https://github.com/void-linux/void-packages/pull/24580#discussion_r509251686

Comment:
Eh, I just removed the `INSTALL.msg`, I think this info is probably a better fit for the "Session and Seat Management" void docs page. The seatd man page and the 1 line `run` file should be plenty for most users to figure out how to use it.