Update light.mqtt docs to include 'retain'

JshWright · web-flow · commit bd26868f2c34 · 2017-04-07T09:52:26.000-04:00
The light.mqtt component supports the 'retain' config parameter, which is important for many MQTT based lights. It is referenced in the explanation paragraph, but was not in the config parameter listing.
diff --git a/source/_components/light.mqtt.markdown b/source/_components/light.mqtt.markdown
@@ -45,6 +45,7 @@ Configuration variables:
 - **payload_off** (*Optional*): The payload that represents disabled state. Default is "OFF".
 - **payload_on** (*Optional*): The payload that represents enabled state. Default is "ON".
 - **qos** (*Optional*): The maximum QoS level of the state topic. Default is 0 and will also be used to publishing messages.
+- **retain** (*Optional*): If the published message should have the retain flag on or not.
 - **rgb_command_topic** (*Optional*): The MQTT topic to publish commands to change the light's RGB state.
 - **rgb_state_topic** (*Optional*): The MQTT topic subscribed to receive RGB state updates.
 - **rgb_value_template** (*Optional*): Defines a [template](/topics/templating/) to extract the RGB value.
