Quality Control assistants supervised voluntary player workouts, advised players on plays/technique, and watched film with the players, which is not allowed.
It's basically very little compared to what the Detroit Free Press accused them. All of the activities in question were voluntary, but according to the NCAA those activities cannot be supervised. Michigan also admitted to going over Sunday practice limits by 20 minutes because of confusion over pre-practice stretching.
It sounds minor (because it is), but apparently the NCAA takes these issues very seriously. Chances are this will end up being a slap on the wrist, but if the NCAA decides to be total dicks and count our basketball probation towards this punishment than it could be much worse.