Getting started guide.

This is the getting started guide. Some of this information exists on the front page of the driver, and some of it is spread out across the cluster and policy files. Let me know if there is more you would expect in a getting started guide. 

How to:
 1. Setup a cluster and get a session
 2. Execute queries on that session (with block and async calls)
 3. Understanding how session's execute a query with a load balancing policy

I plan on adding sections to the index.rst related to some of these topics:

Retry Policies
Setting up SSL
Queries and DataType mappings with python
How to use tracing and gotchas