We want a user-facing manual which contains system emulation
documentation. Create an empty one which we can populate.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20200116141511.16849-3-peter.maydell@linaro.org