Andrew shows us just how easy it is to set up external display support. Though it's easy to set up, getting it to work exactly how you want it is a little more in depth. You will need to monitor for when the display is plugged in and disconnected along with dealing with multitasking limitations.
...it’s wildly simple. Make a window, add a root view controller to it, and set the window’s screen to the external screen
Adding External Display Support To Your iOS App Is Ridiculously Easy by Andrew Fitzpatrick