docs: def ensure_storage_format(root_dir):
      """Checks if the directory looks like a filetracker storage.
      
      Exits with error if it doesn't.
      """
      if not os.path.isdir(os.path.join(root_dir, 'blobs')):
          print('"blobs/" directory not found')
          sys.exit(1)
  
      if not os.path.isdir(os.path.join(root_dir, 'links')):
          print('"links/" directory not found')
          sys.exit(1)
  
      if not os.path.isdir(os.path.join(root_dir, 'db')):
          print('"db/" directory not found')
          sys.exit(1)