Projector documentation.

Change-Id: Ib1967fbbb7e9cd4a14e08bbd0edf782539524a37
Reviewed-on: http://review.couchbase.org/43296
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>