Add docs for Fixer.io sensor (#574)

source/_components/sensor.fixer.markdown

@@ -0,0 +1,37 @@
+---
+layout: page
+title: "Fixer.io"
+description: "Instructions how to integrate exchange rates from Fixer.io within Home Assistant."
+date: 2016-06-20 10:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+ha_category: Sensor
+logo: fixer-io.png
+ha_iot_class: "Local Polling"
+ha_release: 0.23
+---
+
+
+The `fixer` sensor will show you the current exchange rate from [Fixer.io](http://fixer.io/) which is using data from the [European Central Bank (ECB)](https://www.ecb.europa.eu).
+
+To get an owerview about the available [currencies](http://api.fixer.io/latest).
+
+To enable this sensor, add the following lines to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  platform: fixer
+  name: EUR
+  base: EUR
+  target: CHF
+```
+
+Configuration variables:
+
+- **name** (*Optional*): Name to use in the frontend.
+- **base** (*Optional*): The symbol of the base currency. Default to USD 
+- **target** (*Required*): The symbol of the target currency.
+