We might as well surface this useful information in the manual so
users can find it easily. It is a fairly simple conversion to rst with
the only textual fixes being QemuOps to QemuOpts.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20210303173642.3805-6-alex.bennee@linaro.org>