conf: add example for AreaBottomEdge on clickpad buttons

Those that use clickpad buttons as buttons can see cursor jumps as the press
on the touchpad - largely caused by the finger changing shape as the
pressure changes and thus moving the hotspot.

Simple fix is to define the clickpad soft button areas as dead areas, but
this cannot be set as general option as it would break for those that use
tapping.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

conf/50-synaptics.conf

@@ -32,6 +32,9 @@ Section "InputClass"
         Identifier "Default clickpad buttons"
         MatchDriver "synaptics"
         Option "SoftButtonAreas" "50% 0 82% 0 0 0 0 0"
+#       To disable the bottom edge area so the buttons only work as buttons,
+#       not for movement, set the AreaBottomEdge
+#       Option "AreaBottomEdge" "82%"
 EndSection
 
 # This option disables software buttons on Apple touchpads.