message: Add citation for TF-Slim.
diff: @@ -909,3 +909,8 @@ slim.evaluation.evaluation_loop(
  ## Authors
  Sergio Guadarrama and Nathan Silberman
  +
  +## Citation
  +"TensorFlow-Slim: a lightweight library for defining, training and evaluating complex models in TensorFlow"
  +S. Guadarrama, N. Silberman, 2016.
  +https://github.com/tensorflow/tensorflow/tree/master/tensorflow/contrib/slim
  