Merge pull request #439 from cshallue/im2txt-readme

Update citation in README.md

im2txt/README.md

 # Show and Tell: A Neural Image Caption Generator
 
-A TensorFlow implementation of the image-to-text model described in
+A TensorFlow implementation of the image-to-text model described in the paper:
 
-*Show and Tell: A Neural Image Caption Generator*
+"Show and Tell: Lessons learned from the 2015 MSCOCO Image Captioning
+Challenge."
 
 Oriol Vinyals, Alexander Toshev, Samy Bengio, Dumitru Erhan.
 
-http://arxiv.org/abs/1411.4555
+*IEEE transactions on pattern analysis and machine intelligence (2016).*
+
+Full text available at: http://arxiv.org/abs/1609.06647
 
 ## Contact
 ***Author:*** Chris Shallue (shallue@google.com).