docs: explain backoffice for testing service (#131)

docs/src/modules/java/pages/access-control.adoc

@@ -119,9 +119,12 @@ can be overwritten on a per method base.
 
 == Backoffice and self invocations
 
-Invocations of methods from the same service, or from the backoffice using the `akka services proxy` command, are always
+Invocations of methods from the same service, or from via the backoffice proxy that is available to developers, are always
 permitted, regardless of what ACLs are defined on them.
 
+TIP: The `akka service proxy` command creates an HTTP proxy that forwards all
+traffic to a service. This allows you to interact with the service as if it was running locally.
+
 == Local development with ACLs
 
 When testing or running in development, by default, all calls to your service will be blocked as ACLs are enabled by default.