If you're planning to use Steroids, you need to use the Steroids Build Service. To create an actual build targeting iOS platforms, please consult their guide on how to do this.
If you just are developing, use the deploy command to get the QR code and scan it with the AppGyver scanner application to load it temporarily to your device. Or if you want to run it in the emulator, start a steroids session from the terminal:
steroids connect
then enter
simulator
once you're in the steroids session and that should start the iOS simulator.
Not sure what you'd need xCode for in this. The beauty of steroids is that there is no iOS specific code for you to maintain (before you start messing with PhoneGap plugins, which is a different ballgame.) You can still open your html pages using xCode if you wish.
If you're asking how to have xCode do this stuff for you, then I could be wrong but I do not think there is a way. I believe the simulator that Steroids starts is the same as the xCode simulator.