README: Update for new machines
README: Update for new machines

Add new sections for the new minnowmax-64 support, and reflect the
layer rename.

Signed-off-by: Tom Zanussi <1c8a3d9fe0daebf50077f18cba0f71e4a3d97b0e@linux.intel.com>

tzanussi/meta-microlinux,tzanussi/meta-microlinux