Add docs for demo

source/_components/demo.markdown

@@ -0,0 +1,41 @@
+---
+layout: page
+title: "Demo platforms"
+description: "Instructions how to use the Platform demos with Home Assistant."
+date: 2016-02-24 07:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: home-assistant.png
+ha_category: Other
+---
+
+
+The `demo` platform allows you use component which are providing a demo of their implementation. The demo entities are dummies but show you how the acutal platform looks like. This way you can run own demonstration instance like the online [Home Assistant demo](https://home-assistant.io/demo/).
+
+Available demo platforms:
+
+- Alarm control panel (`alarm_control_panel`)
+- Binary sensor (`binary_sensor`)
+- Camera (`camera`)
+- Garage door (`garage_door`)
+- Light (`light`)
+- Lock (`lock`)
+- Notification (`notify`)
+- Roller shutter (`rollershutter`)
+- Sensor (`sensor`)
+- Switch (`switch`)
+- Thermostat (`thermostat`)
+
+To integrate a demo platform in Home Assistant, add the following section to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+[component]:
+  - platform: demo
+```
+
+Configuration variables:
+
+- **[component]** (*Required*): The name of the component as stated in the listing above the configuration example.