Add documentation for ruter sensor. (#7379)

* Add documentation for ruter sensor.

* fix missing link

* Fix missing :

* Change stopid to stop_id

source/_components/sensor.ruter.markdown

@@ -0,0 +1,53 @@
+---
+layout: page
+title: "Ruter Public Transport"
+description: "Instructions on how to integrate departure times from Ruter within Home Assistant."
+date: 2018-11-05 00:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: ruter.png
+ha_category: Transport
+ha_iot_class: "Cloud Polling"
+ha_release: "0.83"
+---
+
+The `ruter` sensor will provide you departure information for the larger Oslo area in Norway from the [Ruter][ruter] public transportation service.
+
+This platform is using the [Ruter reisapi API][ruter-api] to gather the information.
+
+To find the `stop_id` you need to visit the [Ruter][ruter] site and search for your stop.
+In the URL after you have searched, there will be an ID right after the `Stoppested/` in a format like this `(2190400)`, the numbers there is what you need to put in the `stop_id:` configuration option.
+
+Add the data to your `configuration.yaml` file as shown in the example:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: ruter
+    stop_id: STOPID
+```
+
+{% configuration %}
+stop_id:
+  description: The stop id for the stop you want to monitor.
+  required: true
+  type: string
+destination:
+  description: A destination name to show only departures that has this as the final stop.
+  required: false
+  type: string
+offset:
+  description: An offset for the next departure time.
+  required: false
+  default: 0
+  type: integer
+name:
+  description: Name of the sensor.
+  required: false
+  type: string
+{% endconfiguration %}
+
+[ruter]: https://ruter.no/reiseplanlegger/Stoppested
+[ruter-api]: http://reisapi.ruter.no/Help