It's a Twitch command (I think from mIRC it's msg # /host streamname). It makes it so that the other person's stream is now displayed on your Twitch page (but still with your chat room).
It seems that jtv (or whatever it's called) sends a message to the chan when someone hosts you: "X is hosting you for Y viewers". When he says, "read host," I think he means do *something* with that message, but I dunno what ;p
