Consider renaming disk-image-builder or vm-image-builder

[cgwalters]

Hi, the term "image" in the context of Kubernetes I'd generally assume to refer to a container (OCI) image. I work on the bootc project which actually bridges the world of container images and disk images, and for this reason across much of the docs where there might be any ambiguity we say either "container image" or "disk image".

Since this project seems to solely be about disk (vm) images, I think it may make sense to rename it for clarity.

The docs say "virtual machine image" but I think "disk" is shorter to say. Up to you of course, could rename to "vm-image-builder" too, or...of course just close this issue!