GH-1549 Added not on using 'spring.main.sources' as environment property

Resolves #1549

docs/src/main/asciidoc/spring-cloud-stream.adoc

@@ -1321,6 +1321,18 @@ spring:
               rabbitmq:
                 host: <host2>
 ----
+NOTE: The `environment` property of the particular binder can also be used for any Spring Boot property, 
+including this `spring.main.sources` which can be useful for adding additional configurations for the 
+particular binders, e.g. overriding auto-configured beans.
+
+For example;
+[source, yaml]
+----
+environment:
+    spring:
+        main:
+           sources: com.acme.config.MyCustomBinderConfiguration
+----
 
 === Binding visualization and control
 Since version 2.0, Spring Cloud Stream supports visualization and control of the Bindings through Actuator endpoints.