Document process around building and testing new containers before pushing them to quay.io

[sssoleileraaa]

Description

For the workstation, we maintain images of our build containers in quay.io for a CI job that runs a reproducible wheels test, but it's not clear why we do this or when to update those containers or how to test. I think some documentation in our wiki or readme would be helpful.

See #317 and #350 for an idea on how this can get confusing.

[eloquence]

Looks like the original motivation was reproducibility breakage with the CircleCI-provided images (#253) which was addressed via #254.

[legoktm]

I removed the custom dockerfiles in 3c81ff8, we now use plain Debian images for everything, and no longer need to push/maintain anything on quay.io!