The custom help() is replaced by a COMMAND() description, and
--introspect-cli is added. The note about invocation as 'installkernel' is
kept as the footer. Verb and option column widths are kept separate, since
the verb table is very wide. --help now goes through the pager, like other
commands with --no-pager.
A separate COMMAND block is included for installkernel, but it is only
used for introspection data.