Update documentation and readme files

Make sure that markdown documentation is up-to-date.

Mobile Apps @ EF Wiki: https://wiki.eurofurence.org/doku.php?id=team:it:app

We should check out what's still up-to-date here, what we want to keep in the wiki and update, as well as what we may want to just get rid of or move to the README.md and /docs folders of the respective repos.