PyTorch CTRL + Style

docs/source/model_doc/ctrl.rst

@@ -1,6 +1,14 @@
 CTRL
 ----------------------------------------------------
 
+CTRL model was proposed in `CTRL: A Conditional Transformer Language Model for Controllable Generation`_
+by Nitish Shirish Keskar*, Bryan McCann*, Lav R. Varshney, Caiming Xiong and Richard Socher.
+It's a causal (unidirectional) transformer pre-trained using language modeling on a very large
+corpus of ~140 GB of text data with the first token reserved as a control code (such as Links, Books, Wikipedia etc.).
+
+This model is a PyTorch `torch.nn.Module`_ sub-class. Use it as a regular PyTorch Module and
+refer to the PyTorch documentation for all matter related to general usage and behavior.
+
 Note: if you fine-tune a CTRL model using the Salesforce code (https://github.com/salesforce/ctrl),
 you'll be able to convert from TF to our HuggingFace/Transformers format using the 
 ``convert_tf_to_huggingface_pytorch.py`` script (see `issue #1654 <https://github.com/huggingface/transformers/issues/1654>`_).