The Starting Session chapter is gone.
There is now a reorganized Getting Started chapter that deals with explaining
sessions, covers UI basics and tells how to add new tracks and busses.
Then there's new Recording chapter that holds sections on recording audio
and explains routing inside and outside Ardour.
All the past material on JACK has been removed. The tuturial now mentions
the PulseAudio backend and clarifies that JACK is not the recommended backend
anymore.