ElasticSearch Connector docs: provide example of using fields that are not at the first level in the "routing" configuration

Under https://docs.couchbase.com/elasticsearch-connector/4.0/configuration.html#custom-routing-and-parentchild-relationships, for the "routing = '/airlineid'" example, we are providing an example of a field for routing that is at the first level of the document. Sometimes customers would like to use second (or higher) level, for example, say they want the routing field to be at a second level, "firstLevelField.secondLevelField", in which case, they'd have to do '/firstLevelField/secondLevelField'