Displays a short text fullscreen

 Screen Message will display a given multi-line message as large as
 possible, fullscreen and black on white. You can specify the text either
 when launching sm, or edit it while the program is running.
 .
 It is useful to send messages across a room, e.g. during an university
 lecture. For fast startup, it is recommended to bind it to a key in your
 Desktop Environment.