Update README
Update README

Add (work-in-progress) build instructions.

Signed-off-by: Ola Jeppsson <793f970c52ded1276b9264c742f19d1888cbaf73@adapteva.com>

peteasa/oh,peteasa/oh,olajep/oh,parallella/oh,parallella/oh,peteasa/oh,parallella/oh,parallella/oh,olajep/oh,olajep/oh,olajep/oh,peteasa/oh