docs: link to Apple developer docs for `app.ready` event (#31583)

Changes some links around. There was no link for `NSUserNotification`, and
`UNNotificationResponse` incorrectly linked to our own `NotificationResponse`
API structure doc.

docs/api/app.md

@@ -36,10 +36,10 @@ Returns:
 * `launchInfo` Record<string, any> | [NotificationResponse](structures/notification-response.md) _macOS_
 
 Emitted once, when Electron has finished initializing. On macOS, `launchInfo`
-holds the `userInfo` of the `NSUserNotification` or information from
-[`UNNotificationResponse`](structures/notification-response.md) that was used to open the
-application, if it was launched from Notification Center. You can also call
-`app.isReady()` to check if this event has already fired and `app.whenReady()`
+holds the `userInfo` of the [`NSUserNotification`](https://developer.apple.com/documentation/foundation/nsusernotification)
+or information from [`UNNotificationResponse`](https://developer.apple.com/documentation/usernotifications/unnotificationresponse)
+that was used to open the application, if it was launched from Notification Center.
+You can also call `app.isReady()` to check if this event has already fired and `app.whenReady()`
 to get a Promise that is fulfilled when Electron is initialized.
 
 ### Event: 'window-all-closed'