RCB will not work on its own. You need the emulators, too.
Also it will not work as you expect without X in the background to manage input.
Please have a look at the Installing RetroPie on osmc as an alternative way to play retrogames on osmc. You can see it as an intermediate solution as Sam promised some closer retrogaming integration in the future.
Put roms in /home/osmc/RetroPie/roms/systemname after installation.