Extend the BertForSequenceClassification docs to mention the special CLS token.

pytorch_pretrained_bert/modeling.py

@@ -930,7 +930,7 @@ class BertForSequenceClassification(BertPreTrainedModel):
 
     Inputs:
         `input_ids`: a torch.LongTensor of shape [batch_size, sequence_length]
-            with the word token indices in the vocabulary(see the tokens preprocessing logic in the scripts
+            with the word token indices in the vocabulary. Items in the batch should begin with the special "CLS" token. (see the tokens preprocessing logic in the scripts
             `extract_features.py`, `run_classifier.py` and `run_squad.py`)
         `token_type_ids`: an optional torch.LongTensor of shape [batch_size, sequence_length] with the token
             types indices selected in [0, 1]. Type 0 corresponds to a `sentence A` and type 1 corresponds to