Add tokenizer_file parameter to PreTrainedTokenizerFast docstring (#12624)

Co-authored-by: Lewis Bails <Lewis.Bails@infomedia.dk>

src/transformers/tokenization_utils_fast.py

@@ -59,6 +59,9 @@ INIT_TOKENIZER_DOCSTRING += """
         tokenizer_object (:class:`tokenizers.Tokenizer`):
             A :class:`tokenizers.Tokenizer` object from 🤗 tokenizers to instantiate from. See :doc:`Using tokenizers
             from 🤗 tokenizers <../fast_tokenizers>` for more information.
+        tokenizer_file (:class:`str`):
+            A path to a local JSON file representing a previously serialized :class:`tokenizers.Tokenizer` object from
+            🤗 tokenizers.
 """
 
 MODEL_TO_TRAINER_MAPPING = {