title: iOS iCloud document change notification
body: <p>Can you, in Swift get a change notification when a document in the apps's iCloud Drive container changes?
  For example I am testing a simple concept where I am storing all app data as a json string in the app's iCloud Drive container and I am loading it when the app launches.  I can retrieve and save the json string on demand on multiple devices, but I am wondering if there is a way to get a change notification sent to an app when the file is changed on another device.
  If so, some direction would be appreciated.</p>