Added Unifi direct doc. (#4004)

* Added Unifi direct doc.

* Added Unifi direct doc

source/_components/device_tracker.unifi_direct.markdown

@@ -0,0 +1,45 @@
+---
+layout: page
+title: "Ubiquiti Unifi direct AP"
+description: "Instructions how to use a Unifi WAP as a device tracker."
+date: 2017-11-17 14:59
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: ubiquiti.png
+ha_category: Presence Detection
+ha_release: 0.59
+---
+
+
+This platform allows you to detect presence by looking at devices connected to a [UniFi AP](http://ubnt.com/unifi-ap/). This device tracker differs form [Ubiquiti Unifi WAP](https://home-assistant.io/components/device_tracker.unifi/) because it doesn't require the Unifi controller software.
+
+To use this device tracker in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+device_tracker:
+  - platform: unifi_direct
+    host: YOUR_AP_IP_ADDRESS
+    username: YOUR_USERNAME
+    password: YOUR_PASSWORD
+```
+
+{% configuration %}
+host:
+  description: The hostname or IP address of your Unifi AP.
+  required: true
+  type: string
+username:
+  description: The username used to connect to your Unifi AP.
+  required: true
+  type: string
+password:
+  description: The password used to connect to your Unifi AP.
+  required: true
+  type: string
+{% endconfiguration %}
+
+See the [device tracker component page](/components/device_tracker/) for instructions how to configure the people to be tracked.
+