Add note on FSM update messages in API docs

README.md

@@ -244,7 +244,7 @@ To set the tail length of logs (the monitor will send back the last `value` char
 
 ### FSMManagingEventHandler
 
-To attempt executing a trigger on the FSM use:
+To attempt executing a trigger on the FSM use (this will also generate an FSM update message):
 ```
 {
     "key": "fsm",
@@ -266,3 +266,16 @@ To force the broadcasting of an FSM update you can use this message:
     }
 }
 ```
+
+This event handler broadcasts FSM update messages after handling commands in the following format:
+```
+{
+    "key": "fsm_update",
+    "data" :
+    {
+        "current_state": ...string...,
+        "valid_transitions": ...array of {"trigger": ...string...} objects...
+    }
+}
+```
+