fix #808

pytorch_transformers/modeling_xlm.py

@@ -424,6 +424,10 @@ XLM_INPUTS_DOCSTRING = r"""
     Inputs:
         **input_ids**: ``torch.LongTensor`` of shape ``(batch_size, sequence_length)``:
             Indices of input sequence tokens in the vocabulary.
+
+            XLM is a model with absolute position embeddings so it's usually advised to pad the inputs on
+            the right rather than the left.
+
             Indices can be obtained using :class:`pytorch_transformers.XLMTokenizer`.
             See :func:`pytorch_transformers.PreTrainedTokenizer.encode` and
             :func:`pytorch_transformers.PreTrainedTokenizer.convert_tokens_to_ids` for details.