Rather than mentioning the requirement for 4.x binaries but not
explaining why (it was assuming an upgrade from 4.x to 5.0-current),
explain when compat options are needed (for running existing host
binaries) in a more general way while using a more modern example
(COMPAT_FREEBSD11 for 11.x binaries). While here, explicitly mention
that a GENERIC kernel should always work.
Reported by: Robert Huff <email@example.com>