Update raylib.h: GeyKeyName prototype

Prototype for GetKeyName, which is already implemented elsewhere.

src/raylib.h

@@ -1178,6 +1178,7 @@ RLAPI bool IsKeyUp(int key);                                  // Check if a key
 RLAPI int GetKeyPressed(void);                                // Get key pressed (keycode), call it multiple times for keys queued, returns 0 when the queue is empty
 RLAPI int GetCharPressed(void);                               // Get char pressed (unicode), call it multiple times for chars queued, returns 0 when the queue is empty
 RLAPI void SetExitKey(int key);                               // Set a custom key to exit program (default is ESC)
+RLAPI const char *GetKeyName(int key);                        // Get name of a QWERTY key on the current keyboard layout (eg returns string "q" for KEY_A on an AZERTY keyboard)
 
 // Input-related functions: gamepads
 RLAPI bool IsGamepadAvailable(int gamepad);                                        // Check if a gamepad is available