Missing help label description

[hhorak]

The help label is used by atomic, but is not documented in this repository. IMO it also caused the issue tracked in https://pagure.io/atomic-wg/issue/267, which was also reported to projectatomic/atomic#967.
Once the dilemma is resolved, we should document this label properly here.

[TomasTomecek]

The current consensus is that help label should contain executable command. Tooling, such as atomic, should then interpret the command and display documentation to user.

[jmtd]

That sounds like it is going to clash with https://github.com/projectatomic/container-best-practices/blob/master/creating/help.adoc