libinput: Add note about multi-user systems

xorg/libinput/post-install

@@ -5,6 +5,11 @@ cat <<EOF
 NOTE: You must be a part of the input group
       for libinput to work.
 
+NOTE: This groups based permissions model may not
+      be suitable if KISS will be used as a multi
+      user system. Further configuration can be
+      done at your own discretion.
+
 -> addgroup USER input
 
 NOTE: You also need xf86-input-libinput.