Add link to TF monotonic_attention to README

Author: craffel

README.md

@@ -1,6 +1,6 @@
 # Online and Linear-Time Attention by Enforcing Monotonic Alignments
 
-#### *NOTE* - A reference implementation of the monotonic attention mechanism is now built into TensorFlow in the `tf.contrib.seq2seq` module.
+#### *NOTE* - A reference implementation of the monotonic attention mechanism is now built into TensorFlow in the `tf.contrib.seq2seq` module.  See [here](https://www.tensorflow.org/api_docs/python/tf/contrib/seq2seq/monotonic_attention) for documentation.
 
 This repository contains an example implementation of the monotonic alignment decoder proposed in ["Online and Linear-Time Attention by Enforcing Monotonic Alignments"](https://arxiv.org/abs/1704.00784), by Colin Raffel, Minh-Thang Luong, Peter J. Liu, Ron J. Weiss, and Douglas Eck (arXiv:1704.00784).