comment/question on ssb support

re: your readme update about noise level due to pwm

I'm still putting hardware together so have not tested yet, but...

For digital modes like psk31, do we really need to (try to) amplitude modulate the output?

See http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll.html 4th paragraph after diagram.
