How to enable `podman` with `services:`?

I am using Qontainers / Podman In Podman GitLab Runner · GitLab which lets me run gitlab-runner together with podman as a Gitlab runner instance.

I am struggling to use that with services: ... . Is there any documentation what is needed to make this work?
I assume the cni-plugins have to be installed and some setup to be made?

Any information on this is appreciated.