📝 improve subdocument field docs markup
📝 improve subdocument field docs markup

Change-Id: If0aa5d3adc936726fbe51093caa9bfed448b621e
Reviewed-on: http://review.couchbase.org/c/couchbase-ruby-client/+/128858
Tested-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

couchbase/couchbase-ruby-client,couchbase/couchbase-ruby-client,couchbase/couchbase-ruby-client