* Add to v7 migration guide

Author: lukebakken

v7-MIGRATION.md

@@ -1,5 +1,17 @@
 # Migrating to RabbitMQ .NET Client 7.x
 
+This document makes note of major changes in the API of this library for
+version 7. In addition to this document, please refer to the comprehensive
+integration test suites
+[here](https://github.com/rabbitmq/rabbitmq-dotnet-client/tree/main/projects/Test/Integration)
+and
+[here](https://github.com/rabbitmq/rabbitmq-dotnet-client/tree/main/projects/Test/SequentialIntegration)
+that demonstrate these changes.
+
+If you have questions about version 7 of this library, please start a new discussion here:
+
+https://github.com/rabbitmq/rabbitmq-dotnet-client/discussions
+
 ## `async` / `await`
 
 The entire public API and internals of this library have been modified to use
@@ -11,3 +23,18 @@ All TAP methods end with an `Async` suffix, and can be `await`-ed.
 
 * `IModel` has been renamed to `IChannel`
 
+## Consuming messages
+
+When a message is delivered to your code via the
+`AsyncEventingBasicConsumer.Received` event or by sub-classing
+`DefaultAsyncConsumer`, please note that the `ReadOnlyMemory<byte>` that
+represents the message body is owned by this library, and that memory is only
+valid for application use within the context of the executing `Received` event
+or `HandleBasicDeliver` method.
+
+If you wish to use this data _outside_ of these methods, you **MUST** copy the
+data for your use:
+
+```
+byte[] myMessageBody = eventArgs.Body.ToArray();
+```