Added level 4 drawing.

concept/Levels.txt

@@ -18,14 +18,17 @@ Task 5: Build-a-bridge 'n' press a button.
 
 *** Level 2 ***
 
-
+One large room with two 9x9 pads: One measures the sum the other the product of
+the boxes. One weight of two 2x2 pads, indicating which pad carries the heavier
+load.
 
 2 -> 3: Staircase
 
 *** Level 3 ***
 
-Colour-stones 
+Colour-stones, 10x10 matrix, 4 wells in each corner.
 
 3 -> 4: Lift
 
 *** Level 4 ***
+