add redirects from index/ -> docker-io/ and for the docker-io_api too

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #5458 from SvenDowideit/add-redirects-for-docker-io-pr-5414

add redirects from index/ -> docker-io/ and for the docker-io_api too