MINOR: Streams upgrade guide section for newly merged KIPs
Reviewers: Bill Bejeck Matthias J. Sax
More details about the new config <code>StreamsConfig#TOPOLOGY_OPTIMIZATION</code> can be found in <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-295%3A+Add+Streams+Configuration+Allowing+for+Optional+Topology+Optimization">KIP-295</a>.
</p>
+ <h3><a id="streams_api_changes_220" href="#streams_api_changes_220">Streams API changes in 2.2.0</a></h3>
+ <p>
+ We've simplified the <code>KafkaStreams#state</code> transition diagram during the starting up phase a bit in 2.2.0: in older versions the state will transit from <code>CREATED</code> to <code>RUNNING</code>, and then to <code>REBALANCING</code> to get the first
+ stream task assignment, and then back to <code>RUNNING</code>; starting in 2.2.0 it will transit from <code>CREATED</code> directly to <code>REBALANCING</code> and then to <code>RUNNING</code>.
+ If you have registered a <code>StateListener</code> that captures state transition events, you may need to adjust your listener implementation accordingly for this simplification (in practice, your listener logic should be very unlikely to be affected at all).
+ </p>
+
+ <p>
+ In <code>WindowedSerdes</code>, we've added a new static constructor to return a <code>TimeWindowSerde</code> with configurable window size. This is to help users to construct time window serdes to read directly from a time-windowed store's changelog.
+ More details can be found in <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-393%3A+Time+windowed+serde+to+properly+deserialize+changelog+input+topic">KIP-393</a>.
+ </p>
+
+ <p>
+ In 2.2.0 we have extended a few public interfaces including <code>KafkaStreams</code> to extend <code>AutoCloseable</code> so that they can be
+ used in a try-with-resource statement. For a full list of public interfaces that get impacted please read <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-376%3A+Implement+AutoClosable+on+appropriate+classes+that+want+to+be+used+in+a+try-with-resource+statement">KIP-376</a>.
+ </p>
+
<h3><a id="streams_api_changes_210" href="#streams_api_changes_210">Streams API changes in 2.1.0</a></h3>
<p>
We updated <code>TopologyDescription</code> API to allow for better runtime checking.
