[emacs-berlin] Hybrid meeting at c-base

[jman]

> I mean, the calendar doesn't help much, does it?  Maybe change the hyperlink with the caption c-base
> to c-base.org or c-base.org/impressum, so that people can more easily navigate to the address, or
> maybe even provide the address Rungestr. 20 10179 Berlin on the emacs berlin website.

I find these suggestions reasonable so I took the liberty of opening a
PR (I don't think I have write rights on the git repo):

https://github.com/emacs-berlin/emacs-berlin.org/pull/23