Just be sure that your GDD aligns with the physical game. The GDD informs design & development and MUST be accurate e.g. from the 'Mechanics & Dynamics' section, "The player’s primary means of interacting with the game are the keys on the keyboard, specifically the ASWD keys for moving left and right and jumping. The player can also attack enemies by pressing the spacebar and interact with NPCs with the P key."
Whereas in your prototype: the S key is not used for movement, the Attack is P (not Spacebar), and there is no mention of an E and O key?