Added roku platform documentation (#486)

source/_components/media_player.roku.markdown

@@ -0,0 +1,29 @@
+---
+layout: page
+title: "Roku"
+description: "Instructions how to integrate Roku into Home Assistant."
+date: 2016-05-16 20:0+0000
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: roku.png
+ha_category: Media Player
+ha_release: 0.20
+---
+
+
+[Roku](http://www.roku.com/) media players will be automatically discovered if you enable [the discovery component]({{site_root}}/components/discovery/).
+
+Roku platform can also be forced to load by adding the following lines to your `configuration.yaml`:
+
+```yaml
+# Example configuration.yaml entry
+media_player:
+  platform: roku
+  host: 192.168.1.10
+```
+
+Configuration variables:
+
+- **host** *Optional*: Use only if you don't want to scan for devices.