add opensky doc (#2431)

source/_components/sensor.opensky.markdown

@@ -0,0 +1,44 @@
+---
+layout: page
+title: "OpenSky Network"
+description: "Instructions on how to integrate OpenSky Network into Home Assistant."
+date: 2017-04-14 10:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: opensky.png
+ha_category: Sensor
+featured: false
+ha_release: 0.43
+ha_iot_class: "Cloud Polling"
+---
+
+The `opensky` sensor allows one to track overhead flights in a given region. It uses crowd-sourced data from the [OpenSky Network](https://opensky-network.org/) public API. It will also fire Home Assistant events when flights enter and exit the defined region.
+
+## Configuration
+
+To enable this sensor, add the following lines to your `configuration.yaml`.
+
+```yaml
+sensor:
+  - platform: opensky
+    radius: 10
+```
+
+Configuration options for the OpenSky Network sensor:
+
+- **radius** (*Required*): Radius of region to monitor, in kilometers
+- **latitude** (*Optional*): Region latitude (defaults to home zone latitude)
+- **longitude** (*Optional*): Region longitude (defaults to home zone longitude)
+- **name** (*Optional*): Sensor name (defaults to `opensky`)
+
+## Events
+
+- **opensky_entry**: Fired when a flight enters the region
+- **opensky_exit**: Fired when a flight exits the region
+
+Both events have two attributes:
+
+- **sensor**: Name of `opensky` sensor that fired the event
+- **callsign**: Callsign of the flight