docs: def add_local(self, source_fpath, version=None, tags=None):
          """Copies a given file into local store as an instance of this dataset.
  
          Parameters
          ----------
          source_fpath : str
              The full path for the source file to use.
          version: str, optional
              The version of the instance of this dataset.
          tags : list of str, optional
              The tags associated with the given instance of this dataset.
  
          Returns
          -------
          ext : str
              The extension of the file added.
          """
          ext = os.path.splitext(source_fpath)[1]
          ext = ext[1:]  # we dont need the dot
          fpath = self.fpath(version=version, tags=tags, ext=ext)
          shutil.copyfile(src=source_fpath, dst=fpath)
          return ext