Add Chapter 6 python files and fix grammar issues in readme

thinkcspy/Chapter-6-Exercises/Python-files/problem16.py

@@ -0,0 +1,20 @@
+# Runestone.Academy thinkcspy course
+# Chapter 6
+# Problem 16
+
+import math
+
+def myPi(iters):
+    # Calculate an approximation of PI using the Madhava
+    # approximation with iters number of iterations
+
+    #your code here
+    apprPi = 0
+    
+    for i in range(iters):
+        term = (-1)**i/((2*i+1)*3**i)
+        apprPi += term
+    
+    return apprPi * math.sqrt(12)
+        
+print(myPi(10))