I believe there are a couple typos or innacuracies in the "readme.txt" file for Futaken Valley Version 0.031.40. 
The Version header at the top still says 0.031.39. Also the "Inside water" operation mentions A or D + Z, however when playing the game, movement in water is controlled by holding any directional movement key A (move left), D (move right), W (look up), S (crouch) and tapping the Space (jump) button to move (or in the case of swimming left or right, to move faster) in the held direction. I understand that this is a very minor issue and that it can be corrected in later versions, I just wanted to bring attention to it.