document "usage" label?

[jmtd]

The "usage" label has recently turned up in rhel75 images:

            "usage": "This image is very generic and does not serve a single use case. Use it as a base to build your own images.",

This caught us by surprise because we hadn't heard of this label before. I wonder whether, if it's going to be used across a bunch of RH images, it ought to be described in this spec.