added cbauth README
added cbauth README

Change-Id: I4f69bd5646ad879808dc2440f50bcd00622962a6
Reviewed-on: http://review.couchbase.org/45897
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

couchbase/cbauth,couchbase/cbauth