MINOR: Fix link to old doc in quickstart (#12129)
MINOR: Fix link to old doc in quickstart (#12129)

In Kafka's quickstart a link points to the 2.5 Kafka Streams demo.
This PR fixes this link.
lindong28/kafka,guozhangwang/kafka,apache/kafka,apache/kafka,lindong28/kafka,apache/kafka,guozhangwang/kafka,guozhangwang/kafka,guozhangwang/kafka,apache/kafka,lindong28/kafka,lindong28/kafka