code: def readme_for(self, subpath):
          
          if subpath is None:
              return self.root_filename
  
          # Join for safety and to convert subpath to normalized OS-specific path
          filename = os.path.normpath(safe_join(self.root_directory, subpath))
  
          # Check for existence
          if not os.path.exists(filename):
              raise ReadmeNotFoundError(filename)
  
          # Resolve README file if path is a directory
          if os.path.isdir(filename):
              return self._find_file(filename)
  
          return filename
docs: Returns the full path for the README file for the specified
          subpath, or the root filename if subpath is None.
  
          Raises ReadmeNotFoundError if a README for the specified subpath
          does not exist.
  
          Raises werkzeug.exceptions.NotFound if the resulting path
          would fall out of the root directory.