Update CHANGELOG.md

Author: michaelklishin

CHANGELOG.md

@@ -14,6 +14,12 @@ Key highlights include:
 
    GitHub issue: [#878](https://github.com/rabbitmq/rabbitmq-dotnet-client/pull/878)
 
+ * Batch publishing using `System.ReadOnlyMemory<byte>` payloads instead of byte arrays.
+ 
+   Contributed by @danielmarbach.
+
+   GitHub issue: [#865](https://github.com/rabbitmq/rabbitmq-dotnet-client/pull/865), [#892](https://github.com/rabbitmq/rabbitmq-dotnet-client/pull/892)
+
 ## Changes Between 6.0.0 and 6.1.0
 
 This release continues with improvements to memory use and object allocations.