WIP: Client-side authentication doc

- [x] Links to appropriate `/ops` docs
- [x] Explanation write-up
- [x] Ruby
- [ ] Python
- [x] Erlang
- [ ] Java
- [ ] curl
Internally, we just ping the server: https://github.com/basho/riak-ruby-client/blob/master/lib/riak/client/beefcake/socket.rb#L195