Port developer docs for zones to end user docs
Port developer docs for zones to end user docs

Zones are mostly a Solidus concept, and the developer docs attempt to
explain how this concept is used in practice. So, it is portable to the
end user documentation as well. There are just a few changes because the
end user documentation's audience is not developers.

pervino/solidus,pervino/solidus,pervino/solidus,pervino/solidus