[STREAMING][KAFKA][DOC] clarify kafka settings needed for larger batches

## What changes were proposed in this pull request?

Minor doc change to mention kafka configuration for larger spark batches.

## How was this patch tested?

Doc change only, confirmed via jekyll.

The configuration issue was discussed / confirmed with users on the mailing list.

Author: cody koeninger <cody@koeninger.org>

Closes #15570 from koeninger/kafka-doc-heartbeat.

docs/streaming-kafka-0-10-integration.md

@@ -48,6 +48,7 @@ Each item in the stream is a [ConsumerRecord](http://kafka.apache.org/0100/javad
 </div>
 
 For possible kafkaParams, see [Kafka consumer config docs](http://kafka.apache.org/documentation.html#newconsumerconfigs).
+If your Spark batch duration is larger than the default Kafka heartbeat session timeout (30 seconds), increase heartbeat.interval.ms and session.timeout.ms appropriately.  For batches larger than 5 minutes, this will require changing group.max.session.timeout.ms on the broker.
 Note that the example sets enable.auto.commit to false, for discussion see [Storing Offsets](streaming-kafka-0-10-integration.html#storing-offsets) below.
 
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