Update fan.mqtt.markdown (#11260)

* Update fan.mqtt.markdown

Update of the documentation. Based on https://github.com/home-assistant/home-assistant/issues/28804 

Otherwise homekit for instance will crash if you don't have "off".

* ✏️ Tweak


Co-authored-by: Klaas Schoute <klaas_schoute@hotmail.com>

source/_integrations/fan.mqtt.markdown

@@ -180,11 +180,11 @@ device:
       type: string
 {% endconfiguration %}
 
-<dkv class='note warning'>
+<div class='note warning'>
 
 Make sure that your topics match exactly. `some-topic/` and `some-topic` are different topics.
 
-</dkv>
+</div>
 
 ## Examples
 
@@ -214,6 +214,7 @@ fan:
     payload_medium_speed: "medium"
     payload_high_speed: "high"
     speeds:
+      - "off"
       - low
       - medium
       - high