Add Chapter 6 python files and fix grammar issues in readme

thinkcspy/Chapter-6-Exercises/Python-files/problem12.py

@@ -0,0 +1,28 @@
+# Runestone.Academy thinkcspy course
+# Chapter 6
+# Problem 12
+
+import turtle
+
+def drawSprite(t, numSides, legLength):
+    angle = 360/numSides
+    
+    for i in range(numSides):
+        t.forward(legLength)
+        t.up()
+        t.forward(-legLength)    
+        t.right(angle)
+        t.down()
+
+
+wn = turtle.Screen()
+
+wn.bgcolor("tan")
+
+avery = turtle.Turtle()
+avery.color("brown")
+
+drawSprite(avery, 15, 120)
+
+    
+wn.exitonclick()