Add documentation for Rejseplanen public transport sensor component (#8109)

* Add documentation for Rejseplanen public transport sensor

* ✏️ Tweaks

* ✏️ Slimmed down example

source/_components/sensor.rejseplanen.markdown

@@ -0,0 +1,77 @@
+---
+layout: page
+title: "Rejseplanen Public Transport"
+description: "Instructions on how to integrate timetable data for danish Rejseplanen within Home Assistant."
+date: 2019-01-09 08:52
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: rejseplanen.png
+ha_category: Transport
+ha_iot_class: "Cloud Polling"
+ha_release: 0.88
+---
+
+The `rejseplanen` sensor will provide you with traveling details for Danish public transport, using timetable data from [Rejseplanen](https://www.rejseplanen.dk/).
+
+## {% linkable_title Configuration %}
+
+Add a sensor to your `configuration.yaml` file as shown in the example:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: rejseplanen
+    stop_id: 'YOUR_STOP_ID'
+```
+
+The `stop_id` can be obtained by looking up the name of the stop at this link: 
+
+<http://xmlopen.rejseplanen.dk/bin/rest.exe/location?format=json&input=STOP_NAME>
+
+find the stop and copy the `id` field with the trailing zeros.
+
+The sensor can filter the timetables by one or more routes, directions and types. The known types are listed in the table below.
+
+| Departure type | Description |
+|--------------|-------------|
+| BUS | Normal bus |
+| EXB | Express bus |
+| M | Metro |
+| S | S-train |
+| REG | Regional train |
+
+{% configuration %}
+stop_id:
+  description: The id of the public transport stop.
+  required: true
+  type: string
+route:
+  description: List of route names.
+  required: false
+  type: string|list
+direction:
+  description: List of directions to filter by.
+  required: false
+  type: string|list
+departure_type:
+  description: List of departure types to filter by.
+  required: false
+  type: string|list
+{% endconfiguration %}
+
+## {% linkable_title Examples %}
+
+A more extensive example on how to use this sensor:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: rejseplanen
+    stop_id: '000045740'
+    route: 'Bus 350S'
+    direction:
+      - 'Herlev St.'
+      - 'Ballerup St.'
+```