qemu-options: try and clarify preferred block semantics

qemu-options: try and clarify preferred block semantics

Try to correct any confusion about QEMU's Byzantine disk options by
laying out the preferred "modern" options as-per:

 "<danpb> (best:  -device + -blockdev,  2nd obsolete syntax: -device +
     -drive,  3rd obsolete syntax: -drive, 4th obsolete syntax: -hdNN)"

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Cc: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Hanna Reitz <hreitz@redhat.com>
Cc: Thomas Huth <thuth@redhat.com>
Message-Id: <20220822165608.2980552-7-alex.bennee@linaro.org>