A Booking Sheet for Shared Apartment Laundry Machines

The idea

My building has two washers for forty units and no way to know if one's free without walking down three flights. I want a simple booking system, a QR code on each machine linking to a shared calendar, so people can reserve a slot and get a text when their load is done. No new hardware, just a way to stop the daily guessing game and the arguments about whose clothes are still sitting in the dryer.