There have been some question about the supported bands and availability
of SIM cards in the matrix chat, so let's add at least that kind of
basic information.

I'm not a POC member, but just adding general knowledge known from prior
events, which is better than an empty section.

* define who "we" is in the context of the section
* hyperlinks to osmcoom wiki pages for relevant technology
* link to etherpad where interested parties can record their location
* some technical clarifications

The B96 is closed behind Oranienburg due to construction work between
Nassenheide und Teschendorf.

https://oranienburg.de/index.php?object=tx,2967.5&ModID=7&FID=2967.4046.1