Example JSON won't function with SG with only 1 server node

The most typical thing that people are going to do when they want to try out Sync Gateway is to start it up with one server node running on the local machine, and even this getting started guide only instructs to set up one. However, with only one node this provided sync gateway config will not function because there are not enough indexing nodes. I recommend adding an entry for `num_index_replicas` as 0 so that at least the person following the guide can start up sync gateway and not be immediately greeted with a fatal error.

Reporter: Jim Borden
E-mail: jim.borden@couchbase.com