Layer documentation

[gandie]

Dropping a few lines here to flush my memory.

Is your feature request related to a problem? Please describe.

People start asking where to read about new layer-update command for example. Pointing to --help only helps a little.

Describe the solution you'd like

Just like the other commands this should be documented here in README, maybe with some examples, best practices and common use cases. Layer diagrams explaining "shadowing / freezing" ( not even sure on term, docs needed! ) objects over layers with example would drive tears into my eyes 😉

Describe alternatives you've considered

Reading help text on cli, experiments with --dry-run and of course reading code itself