Document resolver=/dev/null

[Defenso-QTH]

Currently even resolver=none copies the resolve.conf file over from the host to the jail.
This does not play well with empty jails or jails that have a read-only /etc, for instance.

An option to allow not doing anything about the resolver configuration would be helpful.

[Defenso-QTH]

Looking at the code I found out that this option already exists and is enabled when setting resolver=/dev/null.

This should be documented in the man page.