Revert "removed CNAME"
Revert "removed CNAME"

This reverts commit d85692033cc8a571b0abb78f5e047ef4f288439c.

GDG-Dusseldorf/gdg-dusseldorf.github.io,GDG-Dusseldorf/gdg-dusseldorf.github.io,GDG-Dusseldorf/gdg-dusseldorf.github.io