I'd like to take the opportunity to point out that when people talk about how mobile touch interfaces have "low discoverability", comments like this are exactly what they're talking about.
Of course, this is all on a grade. Control Centre has a medium-low discoverability (given only a visual hint on the lock screen), and is more vital to the iPhone. The 3D Touch cursor movement is a lot less necessary (I know about it but never use it), and is a lot less discoverable. The 3D Touch-from-edge-of-screen-to-switch-between-apps gesture is there as well, but make slightly more discoverable as its easier to accidentally trigger it to learn about it for the first time.
An aside, I actually find the 'advanced' cursor movement, in both the 3D Touch form on iPhone 6s Plus and in the long-press form on the iPad Pro, to be next to impossible to use. I can never reliably figure out what triggers the different modes of it (cursor movement, text selection, etc) and thus barely ever use it.
Pop-up tutorials always make me feel somewhat intruded on and break the transparent assimilation between me and the tech; being reminded you don't completely control this thing in your hand (or on your monitor -- websites fall in the same boat) dampens my trust of a tool.
Maybe including it in tutorials in the system app. But, yeah something would be nice.