Incorrect documentation for running containers

[AlexanderWells-diamond]

The documentation for running containers refers to a "main" tag on built images. The current code workflow has no way to generate such a tag - the only ones it does out of the box are "latest" and the version number for a tag. There is commented out code that can generate images with the "edge" tag, but that still isn't "main".

[gilesknap]

FYI `oci1 registries will also reject capitals in names so the container image URI needs to be lcased too.