MQTT select config to integration key (#22833)

source/_integrations/select.mqtt.markdown

@@ -16,15 +16,38 @@ To enable MQTT Select in your installation, add the following to your `configura
 
 ```yaml
 # Example configuration.yaml entry
+mqtt:
+  select:
+      - command_topic: topic
+        name: "Test Select"
+        options:
+          - "Option 1"
+          - "Option 2"
+```
+
+<a id='new_format'></a>
+
+{% details "Previous configuration format" %}
+
+The configuration format of manual configured MQTT items has changed.
+The old format that places configurations under the `select` platform key
+should no longer be used and is deprecated.
+
+The above example shows the new and modern way,
+this is the previous/old example:
+
+```yaml
 select:
     - platform: mqtt
       command_topic: topic
       name: "Test Select"
       options:
-      	- "Option 1"
-      	- "Option 2"
+       - "Option 1"
+       - "Option 2"
 ```
 
+{% enddetails %}
+
 {% configuration %}
 availability:
   description: A list of MQTT topics subscribed to receive availability (online/offline) updates. Must not be used together with `availability_topic`.