Added a filled square to tile design

I probably will, but I'm still not 100% confident that I know the use-case for a docstring
versus a comment. The quick Google search I did was "comments explain how code works, docstrings
explain what a piece of code does" but that kind of sounds like the same thing to me?

Either way, documentation is super important and while I try to solve a lot of readability by
appropriatly naming variables/functions, somethings a note to myself (let alone someone else) is
really needed to make the code usable again in a timely manner a year/month/week/day later.

tile.py

@@ -1,27 +1,26 @@
 from turtle import *
+import math
 
 def draw_tile(size):
     "Draws one tile, which can be repeated to form a pattern."
     draw_tile_outline(size)
-    draw_squiggle(size)
+    draw_design(size)
 
 def draw_tile_outline(size):
     pencolor("#dddddd")
     square(size)
 
-def draw_squiggle(size):
-    forward(size/4)
+def draw_design(size):
+    forward(size/2)
     pencolor("black")
-    left(90)
-    quarter_arc_right(size/4)
-    quarter_arc_left(size/4)
-    quarter_arc_left(size/4)
-    quarter_arc_right(size/4)
-    left(90)
-    fly(size/4)
-    left(90)
-    fly(size)
-    left(90)
+    fillcolor("black")
+    left(45)
+    begin_fill()
+    square(math.sqrt(2 * ((size / 2) ** 2)))
+    end_fill()
+    left(135)
+    fly(size/2)
+    left(180)
 
 def fly(distance):
     "Moves without drawing."

tile_grid.py

@@ -10,7 +10,12 @@ 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.)
+    The inner-loop draws each tile to fill out a row, after which the turtle goes
+        back to the beginning of the row and then moves up to begin filling out the
+        next row (the outer-loop controls how many times to shift up in the overall
+        grid), continuing this build-row-then-shift process until the complete
+        grid has been created. The turtle finishes the process back in the lower-left
+        corner of the grid that it created.
     """
     for y in range(height):
         for x in range(width):