Add Instructions on how to use and turn off authentication for json rpc.

Add a section within developers that explains how to disable authentication for the json rpc. Very useful during local development.

Also add a section on

• how generate the authentication token,
• important fields
• and format to use when sending the request to the client.

This doesn't currently exist, the only reference to "authentication" is in the engine section of the doc's page which is less than sufficient.