Fixed the readme file for robot_lever.

resources/graphics/robot_lever/readme

@@ -24,6 +24,8 @@ The following are offset by 96 pixels along the x-axis instead of 32.
 vertical left_up
 horizontal left_left
 
-mirrored vertical left_down
+all mirrored, except
-mirrored horizontal left_right
+   right_up
+and
+   left_right.
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