querycmd: Add README with examples

Change-Id: I8c06a99613ee6d7dac6c75506391f2350c8091e8
Reviewed-on: http://review.couchbase.org/43840
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>