MINOR: document restriction against running multiple Streams apps on same state.dir
Reviewers: Leah Thomas Almog Gavra Guozhang Wang
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>
+ <p>
+ Note: Kafka Streams does not support running multiple instances of the same application as different processes on the same physical state directory. Starting in 2.8.0 (as well as 2.7.1 and 2.6.2),
+ this restriction will be enforced. If you wish to run more than one instance of Kafka Streams, you must configure them with different values for <code>state.dir</code>.
+ </p>
+
<h3><a id="streams_api_changes_280" href="#streams_api_changes_280">Streams API changes in 2.8.0</a></h3>
<p>
We extended <code>StreamJoined</code> to include the options <code>withLoggingEnabled()</code> and <code>withLoggingDisabled()</code> in
