Yeah, don't understand why that info isn't in the owner's manual, since incorrect towing can damage the car significantly. There is no clutch/disconnect between the electric motor and the wheels - so even in neutral, when the wheels turn, so does the electric motor. Towing the car wheels down even in neutral will spin the electric motor, and with the car not 'live' no coolant is flowing, and overheating the motor will be an issue. So towing wheels down is not good, no matter what.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch Rial X10-i wheels, EVoInnovate EVSE