Add tips to configure multiple monitors

Guides/i3.md

@@ -13,3 +13,13 @@ Use the _dmenu_ and use the **i3lock** program.
 ## Activate a wifi connection
 
 Start the **nmtui** program in a terminal.
+
+## Multiple monitors
+
+To get information :
+
+`xrandr`
+
+To adjust screen setup :
+
+`xrandr --output HDMI-0 --auto --above DP-0`