The option to recover deleted files and other changes can be found in the Advanced Settings pane. The feature is only available on the Web client, and hasn’t been added to iCloud Settings app on iOS 8 or iCloud Drive app in the preview of iOS 9. It is expected to be added to these platforms at some point however.
To use it on your device, go to iCloud on the Web and log in to your account. Tap on the Settings icon, and find Advanced Settings pane. You will now find the option to recover various kind of data.
Apple is also letting users know how long they have before it permanently deletes a file in the Files tab. It seems that it is giving a period of 30 days with each file, though certain kinds of files are apparently showing some inconsistencies. You would want to be careful while restoring contacts, calendars and reminders, however. For instance if you restore calendars, invitations will be reshared with contacts.
Contacts are stored as database backups (single contacts cannot be restored), and restoring an earlier database will remove changes made since that date. However, iCloud also takes a backup of the current database before restoring to an old one, so users always have the option to roll back changes.
While Apple is yet to add Time Machine to iOS (a highly requested feature), the ability to restore files could come in handy to users. At the time of iOS 8 release, a bug in iCloud Drive had caused many users to lose their documents. The new move is part of company’s efforts to make it possible for users to recover their accidentally files.