Document of kafkaStreams improvement

// kafkaStreams.java

* <p>
* A simple example might look like this:
* <pre>{@code
* Properties props = new Properties();
* props.put(StreamsConfig.APPLICATION_ID_CONFIG, "my-stream-processing-application");
* props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
* props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
* props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());
*
* StreamsBuilder builder = new StreamsBuilder();
* builder.<String, String>stream("my-input-topic").mapValues(value -> String.valueOf(value.length())).to("my-output-topic");
*
* KafkaStreams streams = new KafkaStreams(builder.build(), props);
* streams.start();
* }</pre>