Documentation for Zenoh configuration

[JEnoch]

The goal of this PR is to add a documentation about the way to configure Zenoh for various use cases and deployments.

So far I plan address the following sections:

• Default configuration
• Case of a robot with multiple hosts/boards (e.g. Turtlebot3)
• Connection from/to another host (i.e. router-to-router)
• Direct connection of a remote Node (e.g. remote rviz)
• Automatic discovery and interconnections of Zenoh routers (i.e. routers scouting)
• Remote connection via a Zenoh router in the cloud
• No router, UDP multicast scouting, single host (i.e. DDS-like, single host)
• No router, UDP multicast scouting, multiple hosts (i.e. DDS-like, multi hosts)
• Downsampling
• Access Control (by network interface)

Any comment or suggestion of additional section is welcome !

[JEnoch]

Also, I'm not sure yet how to re-organize the main README.md to avoid duplicate and to point to this new doc...