[openhabcloud] Update Notification Docs

bundles/org.openhab.io.openhabcloud/README.md

@@ -85,6 +85,8 @@ Note: The optionally exposed items will show up after they receive an update to
 
 The openHAB Cloud Connector allows to send push notifications to apps on mobile devices registered with an [openHAB Cloud instance](https://github.com/openhab/openhab-cloud) such as [myopenHAB.org](https://www.myopenhab.org).
 
+![Push Notification](doc/notifications.png)
+
 To send push notifications, the notification actions have to be used in rules.
 
 ### Basic Usage
@@ -138,7 +140,7 @@ The additional parameter for these variants have the following meaning:
 - `title`: The title of the notification. Defaults to "openHAB" inside the Android and iOS apps.
 - `referenceId`: A user supplied id to both replace existing messages when pushed, and later remove messages with the `hideNotificationByReferenceId` actions.
 - `onClickAction`: The action to be performed when the user clicks on the notification. Specified using the [action syntax](#action-syntax).
-- `mediaAttachmentUrl`: The URL of the media attachment to be displayed with the notification. This can either be a fully qualified URL, prefixed with `http://` or `https://` and reachable by the client device, or an image item with the format `item:MyImageItem`
+- `mediaAttachmentUrl`: The URL of the media attachment to be displayed with the notification. This can either be a fully qualified URL, prefixed with `http://` or `https://` and reachable by the client device, a relative path on the user's openHAB instance starting with `/`, or an image item with the format `item:MyImageItem`
 - `actionButton1`: The action to be performed when the user clicks on the first action button. Specified as `Title=$action`, where `$action` follows the [action syntax](#action-syntax).
 - `actionButton2`: The action to be performed when the user clicks on the second action button. Specified as `Title=$action`, where `$action` follows the [action syntax](#action-syntax).
 - `actionButton3`: The action to be performed when the user clicks on the third action button. Specified as `Title=$action`, where `$action` follows the [action syntax](#action-syntax).