Move Nest sensor configuration to Nest component (#1650)

* Move Nest sensor configuration to Nest component

* Remove support for empty monitored condion list

* Add Nest sensors by default with opt-out

source/_components/sensor.nest.markdown

@@ -16,21 +16,20 @@ ha_release: pre 0.7
 The `nest` sensor platform lets you monitor sensors connected to your [Nest](https://nest.com) devices.
 
 <p class='note'>
-You must have the [Nest component](/components/nest/) configured to use these sensors.  The `nest` binary sensor will automatically be setup when you do.
+You must have the [Nest component](/components/nest/) configured to use these sensors. The sensors will be setup if the `nest` component is configured and the required configuration for the `nest sensor` is set.
 </p>
 
-To customize which sensors are enabled, you can add the following to your `configuration.yaml` file:
-
+To enable sensors and customize which sensors are setup, you can extend the [Nest component](/components/nest/) configuration in your `configuration.yaml` file with the following settings:
 ```yaml
 # Example configuration.yaml entry
-sensor:
-  - platform: nest
+nest:
+  sensors:
     monitored_conditions:
       - 'temperature'
       - 'target'
 ```
 
-If you leave `monitored_conditions` blank, all sensors that are available for your devices will be included.
+By default all sensors for your available Nest devices will be monitored. Leave `monitored_conditions` blank to disable all sensors for the [Nest component](/components/nest/).
 
 Configuration variables:
 
@@ -46,6 +45,7 @@ The following conditions are available by device:
   - hvac\_state: The currently active state of the HVAC system, `heating`, `cooling`, or `off`.
 - Nest Protect:
   - co\_status
-  - smoke\_status 
+  - smoke\_status
+  - batter\_health
 - Nest Camera: none