FAQ/Linux: Account for DEs that don't allow setting area to all screens

Author: TechniKris

site/_wiki/FAQ/Linux.md

@@ -93,6 +93,12 @@ OpenTabletDriver's virtual device might be getting picked up by your desktop env
 
 To fix it, check your desktop environment's tablet settings page and, if possible, make sure the virtual device is mapped to all screens.
 
+If it doesn't let you map the area to more than one screen, you will have to map the area to all screens in OpenTabletDriver:
+
+- `Right click` the area editor
+- Select `Set to display` -> `Virtual Display`
+- Save or apply your settings, and then try mapping your area to the desired monitor in your desktop environment's settings.
+
 ## Tablet is working but there is no pressure {#artist-mode}
 
 Pressure support is available by changing the output mode of OpenTabletDriver to Artist Mode: