Add Chapter 6 python files and fix grammar issues in readme

thinkcspy/Chapter-6-Exercises/Python-files/problem3.py

@@ -0,0 +1,25 @@
+# Runestone.Academy thinkcspy course
+# Chapter 6
+# Problem 3
+
+import turtle
+
+def drawPolygon(t, sideLength, numSides):
+    """Make turtle t draw a polygon."""
+    angle = 360/numSides
+    
+    for i in range(numSides):
+        t.forward(sideLength)
+        t.left(angle)
+
+
+wn = turtle.Screen()
+wn.bgcolor("lightgreen")
+
+tess = turtle.Turtle()
+tess.color("pink")
+tess.pensize(2)
+
+drawPolygon(tess,50,8) 
+
+wn.exitonclick()