Added description to python spark Pi example

docs/index.md

@@ -44,6 +44,9 @@ launching applications). For example,
 
     ./bin/run-example SparkPi 10
 
+The above example runs the Monte Carlo method to estimate the value of Pi. The arguement passed
+(i.e. 10 in this case) is the number of partitions in the RDD.
+
 You can also run Spark interactively through a modified version of the Scala shell. This is a
 great way to learn the framework.
 

examples/src/main/python/pi.py

@@ -27,12 +27,16 @@
 if __name__ == "__main__":
     """
         Usage: pi [partitions]
+
+        Monte Carlo method is used to estimate Pi in the below example.
     """
     spark = SparkSession\
         .builder\
         .appName("PythonPi")\
         .getOrCreate()
 
+    # If no arguments are passed(i.e. `len(sys.argv) < = 1` )
+    # while calling this script, the default value assigned is 2
     partitions = int(sys.argv[1]) if len(sys.argv) > 1 else 2
     n = 100000 * partitions