rootston: add arbitrary libinput config 'tap_enabled'

This ought to be enough to serve as an example for other compositors to
use.

rootston/rootston.ini.example

@@ -30,6 +30,7 @@ theme = default
 map-to-output = VGA-1
 # Restrict cursor movements for this mouse to concrete rectangle
 geometry = 2500x800
+# tap_enabled=true
 
 [keyboard]
 meta-key = Logo