I used this link (create an Automated Build) from this guide.
The browser error console shows:
https://hub.docker.com/v2/repositories/github//autobuild/
Failed to load resource: the server responded with a status of 403 (FORBIDDEN)
I got this hint from https://github.com/docker/hub-feedback/issues/411#issuecomment-149878749
I replaced the following URL with my values.
https://hub.docker.com/add/automated-build/github/form/<GITHUB USER ID>/<GITHUB REPO NAME>/?namespace=<DOCKERHUB NAMESPACE>
This workaround has been outdated. The url returns a 404. Imho, this has to do with dockerhub changing some policies, concerning 'classic' autobuilds & company/user setup.