Add a section for Protocol documentation

In a micro-service architecture such as that of our project, a lot of protocols may be defined to talk between components. The aim of such a documentation is mostly to be informative for other potential developers in the projects. As such it must explain:

• The intent of the protocol (and why the need of this protocol)
• Which components are involved
• Where do the commands come from, where do they go
• What transmission medium (if any) was chosen, and why

For each command, we also expect:

• Intent of the command
• Expected requests and expected responses
• Description of the Data format in the transmission