Add References section to main doc

References section will list all the documents that have been referred for the design

Change-Id: I59c7992b92dece49484e545da41cedd150a823c7
Reviewed-on: http://review.couchbase.org/34469
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Tested-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>