Client docs improvement [JIRA: CLIENTS-1056]

[lukebakken]

http://basho.github.io/riak-python-client/client.html#client-connections

From that page:

The below instantiation statements are all equivalent:

that statement is incorrect as this code starts a client using pbc:

RiakClient()

While all the others establish an http client.

The examples should be consistent and show code for each protocol.

Thanks for reporting this @kaitcarter