Add two new models from QNAP to the help text.  They are compatible
with the TS-119/TS-219 and therefore supported by the current code.
The only difference is that they have less RAM (256 MB instead of
512 MB), a slower CPU (800 MHz vs 1.2 GHz) and a plastic case.

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>