Updating a readme

Author: Evanthx

core/src/main/java/io/temporal/samples/nexus_messaging/callerpattern/README.md

@@ -1,10 +1,11 @@
 ## Entity pattern
 
-The handler worker starts a single `GreetingWorkflow` with a fixed workflow ID.
-`NexusGreetingServiceImpl` holds that ID and routes every Nexus operation to it. The caller's
-inputs contain only business data — no workflow IDs.
+The handler worker starts a `GreetingWorkflow` for a user ID.
+`NexusGreetingServiceImpl` holds that ID and routes every Nexus operation to it. 
+The caller's input does not have that workflow ID as the caller doesn't know it - but the caller sends in the User ID,
+and `NexusGreetingServiceImpl` knows how to get the desired workflow ID from that User ID (see the getWorkflowId call).
 
-Refer to the on demand pattern examples and you will see how to expand this example to not just a single fixed workflow ID - the NexusGreetingServiceImpl simply needs to be able to map something from the inputs to a Workflow ID. For example if the workflow ID is a user ID with a prefix, then if the Nexus inputs include a User ID, then Nexus can simple prepend the same string to get the desired workflow ID.
+HandlerWorker is using the same getWorkflowId call to generate a workflow ID from a user ID when it launches the workflow.
 
 The caller workflow:
 1. Queries for supported languages (`getLanguages` — backed by a `@QueryMethod`)