Added room tracker docs (#810)

* Added page for the new room tracker component

* Added info about using it together with Owntracks

* Updated room presence documentation to new sensor implementation

* Changed name to mqtt_room

* Changed category to Presence Detection

source/_components/sensor.mqtt_room.markdown

@@ -0,0 +1,54 @@
+---
+layout: page
+title: "MQTT Room Presence"
+description: "Instructions on how to track room presence within Home Assistant."
+date: 2016-08-21 03:58
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: mqtt.png
+ha_category: Presence Detection
+ha_release: 0.27
+ha_iot_class: depends
+---
+
+
+The `mqtt_room` sensor platform allows you to detect the indoor location of devices using MQTT clients.
+
+To use this device tracker in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  platform: mqtt_room
+  device_id: 123testid
+  name: 'Cool device'
+  state_topic: 'room_presence'
+  timeout: 5
+```
+
+Configuration variables:
+
+- **device_id** (*Required*): The device id to track for this sensor.
+- **name** (*Optional*): The name of the sensor.
+- **state_topic** (*Optional*): The topic that contains all subtopics for the rooms.
+- **timeout** (*Optional*): The time in seconds after which a room presence state is considered old. An example: device1 is reported at scanner1 with a distance of 1. No further updates are sent from scanner1. After 5 secoonds scanner2 reports device with a distance of 2. The old location info is discarded in favor of the new scanner2 information as the timeout has passed.
+
+Example JSON that should be published to the room topics:
+
+```json
+{
+  "id": "123testid",
+  "name": "Test Device",
+  "distance": 5.678
+}
+```
+
+### {% linkable_title Setting up clients %}
+
+This component works with any software that is sending data in the given format.
+Each client should post the discovered devices in its own subtopic of the configured topic.
+Instead of developing your own application, you can also use any of these already existing clients:
+
+- [**room-assistant**](https://github.com/mKeRix/room-assistant): looks for Bluetooth LE beacons, based on Node.js