mention dependency on seriesly database in README
mention dependency on seriesly database in README

Change-Id: Ie3a506361d9444371618842858a0815de6d66100
Reviewed-on: http://review.couchbase.org/24753
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Pavel Paulau <dd88eded64e90046a680e3a6c0828ceb8fe8a0e7@gmail.com>

ronniedada/litmus,couchbase/cbmonitor,vmx/cbagent,ronniedada/litmus,mikewied/cbagent,couchbase/cbmonitor,pavel-paulau/cbagent,couchbase/cbagent