Add example for how to use the RPC functionality

I decided to create a full example of how to use the RPC functionality. This could really benefit others showing a clear example of the full process involved.

Earlier I opened an issue in this other library (https://github.com/hashicorp/net-rpc-msgpackrpc) as I thought their functionality was a duplication of yours. He didn't know your library implemented RPC as the documentation was lacking in that area. This example will help him understand how to use it.

I will now go on and use your RPC in my own application (as discussed in an earlier issue.) Thanks!