loli10K

This is just an updated version of #1480 since the original author doesn't seem to be active anymore on GitHub. There are still some things to be done: - [x]...

Document how to enable the virtual whiteboard. Needs https://github.com/jitsi/docker-jitsi-meet/pull/1794 to be merged first, probably. This was requested here: https://github.com/jitsi/docker-jitsi-meet/pull/1480#discussion_r1129067361