add model badge

README.md

@@ -5,6 +5,7 @@ Tensorpack is a training interface based on TensorFlow.
 [![Build Status](https://travis-ci.org/ppwwyyxx/tensorpack.svg?branch=master)](https://travis-ci.org/ppwwyyxx/tensorpack)
 [![ReadTheDoc](https://readthedocs.org/projects/tensorpack/badge/?version=latest)](http://tensorpack.readthedocs.io/en/latest/index.html)
 [![Gitter chat](https://badges.gitter.im/gitterHQ/gitter.png)](https://gitter.im/tensorpack/users)
+[![model-zoo](https://img.shields.io/badge/model-zoo-brightgreen.svg)](http://models.tensorpack.com)
 
 See some [examples](examples) to learn about the framework. Everything runs on multiple GPUs, because why not?