KAFKA-15448: Update upgrade guide for KIP-988 (apache#15039)

Reviewers: Colt McNealy <[email protected]>, A. Sophie Blee-Goldman <[email protected]>, Matthias J. Sax <[email protected]>

docs/streams/upgrade-guide.html

@@ -134,6 +134,12 @@ <h3 class="anchor-heading"><a id="streams_notable_changes" class="anchor-link"><
     </p>
 
     <h3><a id="streams_api_changes_370" href="#streams_api_changes_370">Streams API changes in 3.7.0</a></h3>
+    <p>
+        We added a new method to <code>KafkaStreams</code>, namely <code>KafkaStreams#setStandbyUpdateListener()</code> in
+        <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-988%3A+Streams+Standby+Update+Listener">KIP-988</a>,
+        in which users can provide their customized implementation of the newly added <code>StandbyUpdateListener</code> interface to continuously monitor changes to standby tasks.
+    </p>
+
     <p>
         IQv2 supports <code>RangeQuery</code> that allows to specify unbounded, bounded, or half-open key-ranges, which return data in unordered (byte[]-lexicographical) order (per partition).
         <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-985%3A+Add+reverseRange+and+reverseAll+query+over+kv-store+in+IQv2">KIP-985</a> extends this functionality by adding <code>.withDescendingKeys()</code> and <code>.withAscendingKeys()</code>to allow user to receive data in descending or ascending order.