Forgot to mention that you need to change a couple of settings on your phone to enable developer mode
But that’s it
Discussion
If you in test flight we still have 58 days of 1.5(4) which works fine for zapping. So no rush in getting altstore set up.
I recommend going though the altstore process and set up their Nintendo emulator first, nice added bonus to play some roms on iPhone. Once you got that process down, there are a couple of things you gotta set up for sideloading in general like the mail plug-in & dev mode as mentioned above, then adding sideus should be simple.