Add hydro data sensor docs (#566)

source/_components/sensor.swiss_hydrological_data.markdown

@@ -0,0 +1,35 @@
+---
+layout: page
+title: "Swiss Hydrological Data"
+description: "Instructions how to integrate hydrological data of Swiss waters within Home Assistant."
+date: 2016-06-17 17:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+ha_category: Sensor
+ha_iot_class: "Local Polling"
+ha_release: 0.22
+---
+
+
+The `swiss_hydrological_data` sensor will show you details (temperature, level, and discharge) of rivers and lakes in Switzerland.
+
+The [station overview](http://www.hydrodaten.admin.ch/en/danger-levels-table.html) contains a list of all available measuring points and will help to determine the ID of station which is needed for the configuration.
+
+To enable this sensor, add the following lines to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  platform: swiss_hydrological_data
+  name: Aare
+  station: STATION_ID
+```
+
+Configuration variables:
+
+- **name** (*Optional*): Name to use in the frontend.
+- **station** (*Required*): The ID of the measurement point.
+
+The hydrological measurings are coming from the [Swiss Federal Office for the Environment (FOEN)](http://www.hydrodaten.admin.ch).