The https://f-droid.org servers are still unbearably slow, which makes
the initial user-experience miserable.

Using this mirror as default should have no negative consequences.
Official mirrors are still pulled in by the repo index, used for apk
downloads, but the index is now pulled from this mirrpr instead.

ftp.fau.de is one of the f-droid push mirrors, so it gets updated just
at the same time as the f-droid.org repo does.