README updates for HW backend support
README updates for HW backend support

The project README gives instructions on how to build/run Asylo using
the simulation backend. This change updates it to also show how to
build for the SGX HW backend.

PiperOrigin-RevId: 213320618

google/asylo,google/asylo,google/asylo,google/asylo,google/asylo,google/asylo