Add initial docs for recorder

source/_components/recorder.markdown

@@ -0,0 +1,29 @@
+---
+layout: page
+title: "Recorder"
+description: "Instructions how to configure the data recorder for Home Assistant."
+date: 2016-05-21 09:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: home-assistant.png
+ha_category: "History"
+featured: true
+ha_release: "0.20"
+---
+
+The `recorder` component is storing details in the local database which then are handled by the [`history` component](/component/history/).
+
+To setup the `recorder` component in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+recorder:
+  purge_days: DAYS
+```
+
+Configuration variables:
+
+- **purge_days** (*Optional*): Delete events and states older than x days.
+