Mark "code in the Hub" API as experimental (#15624)

src/transformers/tokenization_utils_base.py

@@ -3417,6 +3417,12 @@ class PreTrainedTokenizerBase(SpecialTokensMixin, PushToHubMixin):
         Register this class with a given auto class. This should only be used for custom tokenizers as the ones in the
         library are already mapped with `AutoTokenizer`.
 
+        <Tip warning={true}>
+
+        This API is experimental and may have some slight breaking changes in the next releases.
+
+        </Tip>
+
         Args:
             auto_class (`str` or `type`, *optional*, defaults to `"AutoTokenizer"`):
                 The auto class to register this new tokenizer with.