Describe optional and required environment variables

[luebken]

Describing environment variables shouldn't be exclusive to the nulecule spec https://github.com/projectatomic/ContainerApplicationGenericLabels/blob/master/vendor/projectatomic/labels.md

[TomasTomecek]

It would be great to have those mentioned in a parsable label. We definitely need to have them mentioned in a container image help file.

[goern]

just on a technical level, @TomasTomecek does the proposal mentioned by matthias sufficient?

If so, do we have a need to rename the namespace? Just being nostalgic, but I like the namespace name :)

[TomasTomecek]

Honestly? I would make it shorter, e.g. io.projectatomic.environment.required. On the other hand I'm also fine with the proposal. But you need to get acks from real maintainers here as I'm not one.