Deadlift 1x5 vs 5x5
Deadlift is 1x5 - one heavy set of 5 reps after your warmup. You can read why here: http://stronglifts.com/deadlift/1x5vs5x5/
Doing more than 1x5 Deadlifts is not recommended when Squatting 5x5 3x/week. But if you want to do it anyway, you can create a custom assistance exercise for it. You can do this in settings - assistance - tap the button to create an exercise here. Call it 5x5 Deadlifts and put 5x5 as sets and reps. Then leave the main Deadlifts blank so they're marked as skipped.
The custom 5x5 Deadlifts won't show on your graphs and the workout will always show the empty 1x5 Deadlifts. But outside of this the app will progress your custom 5x5 Deadlifts fine