FlinkKafkaProducer011 and Flink 1.4.0 Kafka docs

[Elias Levy]

Looks like the Flink Kafka connector page, in the Producer section
<https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/connectors/kafka.html#kafka-producer>,
is missing a section for the new FlinkKafkaProducer011 producer.  Given
that the new producer no longer has a static writeToKafkaWithTimestamps
method, it would be good to add a section that specifies that you must now
use DataStream.addSink.