desktop/dwm: Update README.CONFIG.

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackbuilds.org>

desktop/dwm/README.CONFIG

@@ -19,6 +19,27 @@ with a small point.
 
 dwm draws a small border around windows to indicate their focus state.
 
+
+MULTI-MONITOR SETUP
+-------------------
+
+In multi-monitor situations, you will probably need to run some
+xrandr settings. For example, considering a laptop with an external
+monitor to the right of it, the following command would 'extend' the
+display (rather than the default mirroring), and set the correct
+resolution for both displays:
+
+  $ xrandr --auto --output LVDS --primary --mode 1366x768 \
+  --left-of VGA-0 --output VGA-0 --mode 1280x1024
+
+To determine your optimal resolutions and display names, simply run:
+
+  $ xrandr -q
+
+To make this change permanent simply place the xrandr command before
+'exec dwm' in your '.xinitrc'.
+
+
 CUSTOMIZATION
 -------------
 If you wish to make changes to the default keybindings or other