Add 0.7.4 release blog post

source/components/alarm_control_panel.mqtt.markdown

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+---
+layout: page
+title: "MQTT alarm support"
+description: "Instructions how to integrate MQTT alarms into Home Assistant."
+date: 2015-09-14 19:10
+sidebar: false
+comments: false
+sharing: true
+footer: true
+---
+
+<img src='/images/supported_brands/mqtt.png' class='brand pull-right' />
+This platform enables the possibility to control an MQTT alarm. The alarm will only change state after
+receiving the a new state from `state_topic`. If these messages are published with RETAIN flag, the MQTT
+alarm will receive an instant state update after subscription and will start with correct state. Otherwise,
+the initial state will be `unknown`.
+
+```yaml
+# Example configuration.yaml entry
+alarm_control_panel:
+  platform: mqtt
+  state_topic: "home/alarm"
+  command_topic: "home/alarm/set"
+  name: "MQTT Alarm"
+  qos: 0
+  payload_disarm: "DISARM"
+  payload_arm_home: "ARM_HOME"
+  payload_arm_away: "ARM_AWAY"
+  code: "mySecretCode"
+```
+
+Configuration variables:
+
+- **state_topic** (*Required*): The MQTT topic subscribed to receive state updates.
+- **command_topic** (*Required*): The MQTT topic to publish commands to change the alarm state.
+
+- **name** (*Optional*): The name of the alarm. Default is 'MQTT Alarm'.
+- **qos** (*Optional*): The maximum QoS level of the state topic. Default is 0. This QoS will also be used to publishing messages.
+- **payload_disarm** (*Optional*): The payload do disarm alarm. Default is "DISARM".
+- **payload_arm_home** (*Optional*): The payload to set armed-home mode. Default is "ARM_HOME".
+- **payload_arm_away** (*Optional*): The payload to set armed-away mode. Default is "ARM_AWAY".
+- **code** (*Optional*): If defined, specifies a code to enable or disable the alarm in the frontend.
+