Where do I put the root dialog for a Microsoft Bot Service

Question

I am a complete N00b when it comes to creating a bot service. I have generated my bot using the Basic Template. In the template code the run.csx file starts the code with the

public static async Task<object> Run(HttpRequestMessage req, TraceWriter log) 

method. There are many people that point to the PizzaBot for reference but I can not tell what code is called first to kick off the Dialog Flow. Where would I start the dialog chain ? Do I replace this logic

....

case ActivityTypes.Message:
          await Conversation.SendAsync(activity, () => new EchoDialog());
            break;
....

with

await Conversation.SendAsync(activity, () => new RootDialog());

or somewhere completely different. Just trying to figure out where to create the root dialog to start the process and all the samples I have seen do not have a run.csx and I have no idea how the service is getting started.