Containerized warewulfd build and documentation

[anderbubble]

Warewulf includes a Dockerfile, but I don't think we have instructions for running Warewulf from Podman (or Docker). We should add those, which may also include building the container and publishing it as an artifact, likely on Github (similar to how we do for node images).

[anderbubble]

@mslacken I know you've been working on this; is the Dockerfile that's there already fit for this purpose, or is there more dev to do?

[mslacken]

It should be fit for this purpose but needs testing.