Area registry (#172)

* Add documentation for area registry
Update device attributes with area id

* If not saving stuff can't be commited
Second try at adding area id info to device registry

docs/area_registry_index.md

@@ -0,0 +1,11 @@
+---
+title: Area Registry
+sidebar_label: Introduction
+---
+
+The area registry is a registry where Home Assistant keeps track of areas. An area represents a physical location for Home Assistant. It can be used to place devices in different areas.
+
+| Attribute | Description |
+| --------- | ----------- |
+| id | Unique ID of area (generated by Home Assistant)
+| name | Name of this area

docs/device_registry_index.md

@@ -21,6 +21,7 @@ The device registry is a registry where Home Assistant keeps track of devices. A
 | config_entries | Config entries that are linked to this device.
 | sw_version | The firmware version of the device.
 | via_hub | Identifier of a device that routes messages between this device and Home Assistant. Examples of such devices are hubs. This is used to show device topology in Home Assistant.
+| area_id | The Area which the device is placed in.
 
 ## Defining devices
 

website/sidebars.json

@@ -46,6 +46,9 @@
     ],
     "Device Registry": [
       "device_registry_index"
+    ],
+    "Area Registry": [
+      "area_registry_index"
     ]
   },
   "Extending Frontend": {