Document all_handlers_finished in the README

updates_and_signals/safe_message_handlers/README.md

@@ -4,9 +4,9 @@ This sample shows off important techniques for handling signals and updates, aka
 
 * Here, using workflow.wait_condition, signal and update handlers will only operate when the workflow is within a certain state--between cluster_started and cluster_shutdown.
 * You can run start_workflow with an initializer signal that you want to run before anything else other than the workflow's constructor.  This pattern is known as "signal-with-start."
-* Message handlers can block and their actions can be interleaved with one another and with the main workflow.  This can easily cause bugs, so we use a lock to protect shared state from interleaved access.
-* Message handlers should also finish before the workflow run completes.  One option is to use a lock.
-* An "Entity" workflow, i.e. a long-lived workflow, periodically "continues as new".  It must do this to prevent its history from growing too large, and it passes its state to the next workflow.  You can check `workflow.info().is_continue_as_new_suggested()` to see when it's time.  Just make sure message handlers have finished before doing so.  
+* Message handlers can block and their actions can be interleaved with one another and with the main workflow.  This can easily cause bugs, so you can use a lock to protect shared state from interleaved access.
+* An "Entity" workflow, i.e. a long-lived workflow, periodically "continues as new".  It must do this to prevent its history from growing too large, and it passes its state to the next workflow.  You can check `workflow.info().is_continue_as_new_suggested()` to see when it's time. 
+* Most people want their message handlers to finish before the workflow run completes or continues as new.  Use `await workflow.wait_condition(lambda: workflow.all_handlers_finished())` to achieve this.
 * Message handlers can be made idempotent.  See update `ClusterManager.assign_nodes_to_job`.
 
 To run, first see [README.md](../../README.md) for prerequisites.