i3: use matrix image as lock screen

i3/multi/config

@@ -9,7 +9,7 @@ floating_modifier $mod
 # start a terminal
 bindsym $mod+Return exec urxvtc
 
-bindsym $mod+b exec i3lock
+bindsym $mod+b exec i3lock -i ~/.config/i3/matrix.png -t
 
 # kill focused window
 bindsym $mod+Shift+q kill

i3/multi/matrix.png

@@ -0,0 +1 @@
+../matrix.png