Add Chapter 6 python files and fix grammar issues in readme

thinkcspy/Chapter-6-Exercises/Python-files/problem18.py

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+# Runestone.Academy thinkcspy course
+# Chapter 6
+# Problem 18	
+
+import turtle
+
+def writeData(tt, height):
+    tt.up()
+    tt.left(90)
+    tt.forward(height+10)
+    tt.right(90)
+    tt.forward(10)
+    tt.write(str(height))
+    tt.forward(30)
+    tt.right(90)
+    tt.forward(height+10)
+    tt.left(90)
+    
+
+def drawBar(t, height):
+    """ Get turtle t to draw one bar, of height. """
+    t.begin_fill()               # start filling this shape
+    t.left(90)
+    t.forward(height)
+    t.right(90)
+    t.forward(40)
+    t.right(90)
+    t.forward(height)
+    t.left(90)
+    t.end_fill()                 # stop filling this shape
+
+
+
+xs = [48, 117, 200, 240, 160, 260, 220]  # here is the data
+maxheight = max(xs)+10
+numbars = len(xs)
+border = 10
+
+wn = turtle.Screen()             # Set up the window and its attributes
+wn.setworldcoordinates(0-border, 0-border, 40*numbars+border, maxheight+border)
+wn.bgcolor("lightblue")
+
+tess = turtle.Turtle()           # create tess and set some attributes
+tess.color("purple")
+tess.fillcolor("magenta")
+tess.pensize(3)
+
+alex = turtle.Turtle()
+alex.color("magenta")
+
+
+for a in xs:
+    drawBar(tess, a)
+    writeData(alex, a)
+
+wn.exitonclick()