[Spark-1261] add instructions for running python examples to doc overview page

Author: Diana Carroll <dcarroll@cloudera.com>

Closes #162 from dianacarroll/SPARK-1261 and squashes the following commits:

14ac602 [Diana Carroll] typo in python example text
5121e3e [Diana Carroll] Add explanation of how to run Python examples to main doc overview page

Author: Diana Carroll

docs/index.md

@@ -23,10 +23,12 @@ For its Scala API, Spark {{site.SPARK_VERSION}} depends on Scala {{site.SCALA_BI
 
 # Running the Examples and Shell
 
-Spark comes with several sample programs in the `examples` directory.
-To run one of the samples, use `./bin/run-example <class> <params>` in the top-level Spark directory
+Spark comes with several sample programs.  Scala and Java examples are in the `examples` directory, and Python examples are in `python/examples`.
+To run one of the Java or Scala sample programs, use `./bin/run-example <class> <params>` in the top-level Spark directory
 (the `bin/run-example` script sets up the appropriate paths and launches that program).
 For example, try `./bin/run-example org.apache.spark.examples.SparkPi local`.
+To run a Python sample program, use `./bin/pyspark <sample-program> <params>`.  For example, try `./bin/pyspark ./python/examples/pi.py local`.
+
 Each example prints usage help when run with no parameters.
 
 Note that all of the sample programs take a `<master>` parameter specifying the cluster URL