Add example using tags and topics

It would be great to have an example that shows a good use case for tags and topics.

Tags: used as a way to indicate to other members of the network how to process the message. For example, is this a new customer order, or is someone cancelling an order?

Topic: used to ensure related messages are processed sequentially in order. For example, all messages related to a certain customer ID may be put on the same topic. This ensures that everything that customer is doing happens in order, and it also means that specific customer's messages will not block another customer's messages.