Added documentation for my Steam sensor

source/_components/sensor.steam_online.markdown

@@ -0,0 +1,50 @@
+---
+layout: page
+title: "Steam"
+description: "Instructions on how to set up Steam sensors in Home Assistant."
+date: 2015-12-19 09:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: steam.png
+ha_category: Sensor
+---
+
+
+The Steam component will allow you to track the online status of public [Steam](https://steamcommunity.com) accounts.
+
+You need an API key	which is [free](https://steamcommunity.com/dev/apikey) to use the component
+
+To find an account's 64-bit SteamID you can check the URL of the profile page, if it ends with a long string on numbers then that's the 64-bit SteamID. However, if the profile has a custom URL you will have to copy the it and enter it into [STEAMID I/O](https://steamid.io/) to find the 64-bit SteamID.
+
+To use Steam in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  platform: steam_online
+  api_key: YOUR_API_KEY
+  accounts:
+    - account1
+    - account2
+```
+
+Configuration variables:
+
+- **api_key** (*Required*): Your API key from [https://steamcommunity.com/dev/apikey](https://steamcommunity.com/dev/apikey).
+- **accounts** array (*Required*): Array of accounts.
+  - **account_id** (*Required*): 64-bit SteamID.
+
+
+If you want to add the accounts to a group for example you will have to use:
+
+```yaml
+# Example configuration.yaml entry
+group:
+  steam:
+    name: Steam
+    entities:
+      - sensor.steam_account1
+      - sensor.steam_account2
+```