add explaination

3: of course, otherwise, i will lose tract on what functions I defined and might be confusing for others.
It's not only for future use, but also for sharing with others.

tile_grid.py

@@ -10,7 +10,8 @@ from tile import fly
 def draw_tile_grid(width, height, tile_size, tile_function):
     """Draws a (width x height) grid, with tile_function drawn on each tile.
 
-    (Your explanation here.)
+    (First, for x in range width, draw a tile defined by tile_size, then draw the curve by calling fly function.
+    After that, return to the original position to repeat the process. When x and y come to the number we input, it will stop.)
     """
     for y in range(height):
         for x in range(width):