greybus: update README with info on how to build and contact me.

Greybus kernel code

To build against the running kernel (odds are you don't want this):

	make

To build against a specific kernel source tree (odds are you want this):

	KERNELDIR=/home/some/random/place make

Any questions / concerns about this code base, please email:

	Greg Kroah-Hartman <greg@kroah.com>