3.13.1 release notes: add an example for channel_max_per_node

Author: michaelklishin

release-notes/3.13.1.md

@@ -56,7 +56,12 @@ Release notes can be found on GitHub at [rabbitmq-server/release-notes](https://
 #### Enhancements
 
  * `channel_max_per_node` is a new per-node limit that allows to put a cap on the number
-   of AMQP 0-9-1 channels that can be concurrently open by all clients connected to a node.
+   of AMQP 0-9-1 channels that can be concurrently open by all clients connected to a node:
+
+   ``` ini
+   # rabbitmq.conf
+   channel_max_per_node = 5000
+   ```
 
    This is a guardrail mean to protect nodes from [application-level channel leaks](https://www.rabbitmq.com/docs/channels#channel-leaks).