Clarify that CORS configuration isn't needed for the Disk service [ci skip]

Author: georgeclaghorn

guides/source/active_storage_overview.md

@@ -524,6 +524,8 @@ Take care to allow:
   * `x-ms-blob-content-disposition` (for Azure Storage only)
   * `x-ms-blob-type` (for Azure Storage only)
 
+No CORS configuration is required for the Disk service since it shares your app’s origin.
+
 #### Example: S3 CORS configuration
 
 ```xml