Add openSenseMap docs

source/_components/air_pollutants.opensensemap.markdown

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+---
+layout: page
+title: "OpenSenseMap"
+description: "Instructions on how to setup openSenseMap sensors in Home Assistant."
+date: 2018-12-15 00:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: opensensemap.png
+ha_category: Health
+ha_release: 0.85
+ha_iot_class: "Cloud Polling"
+---
+
+The `opensensemap` air pollutants platform will query the open data API of [openSenseMap.org](https://opensensemap.org/) to monitor air quality sensor station.
+
+## {% linkable_title Setup %}
+
+To get the ID of a station you need to select it on the [openSense map](https://opensensemap.org/) and find it in the addressbar of your browser. It's the last part of the URL, e.g., `5b450e565dc1ec001bf7cd1d` [https://opensensemap.org/explore/5b450e565dc1ec001bf7cd1d](https://opensensemap.org/explore/5b450e565dc1ec001bf7cd1d).
+
+## {% linkable_title Manual Configuration %}
+
+To enable this platform, add the following lines to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+air_pollutants:
+  - platform: opensensemap
+    station_id: STATION_ID
+```
+
+{% configuration %}
+station_id:
+  description: The ID of the station to monitor.
+  required: true
+  type: string
+name:
+  description: Name of the sensor to use in the frontend.
+  required: false
+  default: Station name
+  type: string
+{% endconfiguration %}
+