Add docs for Android Auto notifications

docs/android-auto/android-auto.md

@@ -22,3 +22,25 @@ In order to use this integration you will need a phone as well as a vehicle with
 - `scene`
 - `script`
 - `switch`
+
+### Notifications <span class='beta'>BETA</span>
+
+By default Home Assistant notifications do not show up in the Android Auto interface. To show Home Assistant notifications in Android Auto, add [`car_ui: true` to the notification data](../notifications/basic.md#android-auto-visibility). Notifications will now show up on your phone _and_ in Android Auto. Opening the notification from Android Auto will open the driving interface for Home Assistant.
+
+Notifications in Android Auto share settings with your phone and do not support all notification features. This means that, for example, to have a notification show on top of the current screen in Android Auto, it will also need to be set to pop up on your phone. For the best experience, it is recommended to use a specific [channel](../notifications/basic.md#notification-channels) for notifications that should be visible in Android Auto. Example:
+
+```yaml
+  - alias: Send door unlocked alert
+    trigger:
+      ...
+    action:
+      - service: notify.mobile_app_<your_device_id_here>
+        data:
+          title: "Door unlocked"
+          message: "Everyone left home but the door is still unlocked"
+          data:
+            car_ui: true
+            notification_icon: "mdi:door-open"
+            channel: "Door unlocked"
+            importance: high
+```

docs/notifications/basic.md

@@ -616,6 +616,23 @@ On Android you also have the option of changing the notification status bar icon
             notification_icon: "mdi:cellphone"
 ```
 
+### Android Auto visibility <span class='beta'>BETA</span>
+
+By default Home Assistant notifications do not show up in the Android Auto interface. By adding `car_ui: true`, notifications will become visible and opening them from Android Auto will start the driving interface. For more details on how notifications work in Android Auto, [review the Android Auto documentation](../android-auto/android-auto.md#notifications).
+
+```yaml
+  - alias: Send door unlocked alert
+    trigger:
+      ...
+    action:
+      - service: notify.mobile_app_<your_device_id_here>
+        data:
+          title: "Door unlocked"
+          message: "Everyone left home but the door is still unlocked"
+          data:
+            car_ui: true
+```
+
 ## iOS/macOS Specific
 
 ### Sounds