Update README.md

README.md

@@ -29,7 +29,8 @@ Collect the following information:
 Supply these values to the ENV vars below. The default data refresh interval is 30 minutes and can be overridden with ONSTAR_REFRESH with values in milliseconds.
 
 * **NEW - Command Response Status is now published to MQTT topics!**
-    * Topic format: homeassistant/{VIN}/command/{CommandName}/state
+    * Topic format: MQTT_PREFIX/{VIN}/command/{CommandName}/state
+        * Note: Unless defined, default MQTT_PREFIX=homeassistant   
 
 ### Docker