Added documentation for new russound_rio platform (#2969)

* Added documentation for new russound_rio platform

* Remove port from example since it is optional

source/_components/media_player.russound_rio.markdown

@@ -0,0 +1,34 @@
+---
+layout: page
+title: "Russound RIO"
+description: "Instructions on how to integrate Russound RIO devices into Home Assistant."
+date: 2017-07-12 22:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: russound.png
+ha_category: Media Player
+ha_release: 0.49
+ha_iot_class: "Local Push"
+---
+
+The `russound_rio` platform allows you to control Russound devices that make use of the RIO protocol.
+
+The platform automatically discovers all enabled zones and sources. Each zone is added as a media player device with the enabled sources available as inputs. Media information is supported if the selected source reports it.
+
+To add a device to your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+media_player:
+  - platform: russound_rio
+    host: 192.168.1.10
+    name: Russound
+```
+
+Configuration variables:
+
+- **host** (*Required*): The IP of the TCP gateway
+- **port** (*Optional*): The port of the TCP gateway (default: 9621)
+- **name** (*Required*): The name of the device