Swift - CloudKit - Create an iCloud account for development.

You’ll need an iCloud account to save records to a CloudKit container. 
You’ll enter the credentials for this iCloud account on the device that you run your app. 
If you don’t have an iCloud account, create one that you can use during development. 
On your Mac, launch System Preferences and click iCloud. Click Create Apple ID under the 
Apple ID text field and follow the instructions.

In development, when you run your app through Xcode on a simulator or a device, you need to 
enter iCloud credentials to read records in the public database. In production, the default 
permissions allow non-authenticated users to read records in the public database but do not 
allow them to write records.