Add MQTT Automation Example (#2070)

* Update input_select.markdown

I added an MQTT automation example similar to the one on the input_slider component page.

* Fixed Typo

Fixed "Exampleof" typo.

source/_components/input_select.markdown

@@ -79,3 +79,49 @@ scene:
       input_select.who_cooks:
         option: Paulus
 ```
+
+Example of `input_select` being used in a bidirectional manner, both being set by and controlled by an MQTT action in an automation.
+
+```yaml
+{% raw %}
+# Example configuration.yaml entry using 'input_select' in an action in an automation
+   
+# Define input_select
+input_select:
+  thermostat_mode:
+    name: Thermostat Mode
+    options:
+      - "auto"
+      - "off"
+      - "cool"
+      - "heat"
+    icon: mdi:target
+
+# Automation.     
+ # This automation script runs when a value is received via MQTT on retained topic: thermostatMode
+ # It sets the value selector on the GUI. This selector also had its own automation when the value is changed.
+- alias: Set Thermostat Mode Selector
+  trigger:
+    platform: mqtt
+    topic: "thermostatMode"
+   # entity_id: input_select.thermostat_mode
+  action:
+     service: input_select.select_option
+     data_template:
+      entity_id: input_select.thermostat_mode
+      option: '{{ trigger.payload }}'
+
+ # This automation script runs when the thermostat mode selector is changed.
+ # It publishes its value to the same MQTT topic it is also subscribed to.
+- alias: Set Thermostat Mode
+  trigger:
+    platform: state
+    entity_id: input_select.thermostat_mode
+  action:
+    service: mqtt.publish
+    data_template:
+      topic: "thermostatMode"
+      retain: true
+      payload: '{{ states.input_select.thermostat_mode.state }}'
+{% endraw %}
+```