Add batinfo sensor docs (#903)

* Add batinfo sensor docs

* Fix typo

* Rename to linux_battery

* Add new configuration variable and update description

source/_components/sensor.linux_battery.markdown

@@ -0,0 +1,31 @@
+---
+layout: page
+title: "Linux Battery"
+description: "Instructions how to integrate Linux Battery information into Home Assistant."
+date: 2016-09-06 07:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+ha_category: System Monitor
+ha_release: 0.28
+ha_iot_class: "Local Polling"
+---
+
+The `linux_battery` sensor platform is using the information stored in `/sys/class/power_supply/` on your local Linux system to display details about the current state of your battery. 
+
+To setup a battery sensor to your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: linux_battery
+    name: Laptop
+    battery: 1
+```
+
+Configuration variables:
+
+- **name** (*Optional*): Friendly name to use for the frontend. Default to "Battery".
+- **battery** (*Optional*): Number of the battery. Default to `1`.
+