Add documentation pointer to README
Add documentation pointer to README

Change-Id: Ibc3798c8d764bf59ce5ef00f115605bcfd03412a
Signed-off-by: Matt Spinler <c000c989d08c98662d98f15448f11de169feb92d@us.ibm.com>

openbmc/phosphor-hwmon,openbmc/phosphor-hwmon