docs: Mention need for stomp config in run subcommand (#1515)

Author: tpoliaw

src/blueapi/cli/cli.py

@@ -337,7 +337,12 @@ def run_plan(
     instrument_session: str,
     parameters: TaskParameters,
 ) -> None:
-    """Run a plan with parameters"""
+    """Run a plan with parameters
+
+    To run in the foreground and block until it is complete, stomp
+    configuration is required. Without stomp configuration, '--bg' can be used
+    to start a plan in the background.
+    """
 
     client = cast(BlueapiClient, obj["client"])
     task = TaskRequest(