L2SS-1444: Added comment

SAS/TMSS/backend/services/lobster/lib/message_handler.py

@@ -159,6 +159,8 @@ class L2TMSSObservationControlMessageHandler(TMSSEventMessageHandler):
             # kickstart the observation on COBALT to start and stop at the
             # times as provided in the parset.
             # first 3 parameters are historical and ignored
+            # NB: This command returns "immediately", that is, COBALT will start the actual observation in the
+            #     background.
             _system(f"ssh {COBALT_HEADNODE} {COBALT_START_SCRIPT} 1 2 3 {COBALT_PARSET_DIR}/{PARSET_FILENAME} {subtask_id}")