Use new URL https://wiki.uberspace.de/ for documentation wiki.

git-svn-id: https://plugins.svn.wordpress.org/uberbar/trunk@924822 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update readme.txt.

git-svn-id: https://plugins.svn.wordpress.org/uberbar/trunk@924823 b8457f37-d9ea-0310-8a92-e5e31aec5664