Explaining how to implement new protocols

[egekorkan]

In the main readme there are the following sentences:

Note: More protocols can be easily added by implementing ProtocolClient, ProtocolClientFactory, and ProtocolServer interface.

Note: More mediaTyes can be easily added by implementing ContentCodec interface.

However, it would be good to explain via examples how this would be done.

P.S. This showed up in the discussion with @jenlincode on 25.02.2020