Update README.md

README.md

 # X2Paddle
 X2Paddle is a toolkit for converting trained model to PaddlePaddle from other deep learning frameworks. 支持主流深度学习框架模型转换至PaddlePaddle（飞桨）
+
+
+## 转换tensorflow vgg_16模型
+
+### 步骤一 下载模型参数文件
+```
+wget http://download.tensorflow.org/models/vgg_16_2016_08_28.tar.gz
+```
+
+### 步骤二 导出vgg_16的pb模型
+使用如下python脚本转换
+```
+import tensorflow.contrib.slim as slim
+from tensorflow.contrib.slim.nets import vgg
+
+def freeze_model(sess, output_tensor_names, freeze_model_path):
+    out_graph = graph_util.convert_variables_to_constants(
+        sess, sess.graph.as_graph_def(), output_tensor_names)
+    with tf.gfile.GFile(freeze_model_path, 'wb') as f:
+        f.write(out_graph.SerializeToString())
+
+    print("freeze model saved in {}".format(freeze_model_path))
+    
+with tf.Session() as sess:
+    inputs = tf.placeholder(dtype=tf.float32,
+                            shape=[None, 224, 224, 3],
+                            name="inputs")
+    logits, endpoint = vgg.vgg_16(inputs, num_classes=1000, is_training=False)
+    load_model = slim.assign_from_checkpoint_fn(
+        "vgg_16.ckpt", slim.get_model_variables("vgg_16"))
+    load_model(sess)
+    
+freeze_model(sess, ["vgg_16/fc8/squeezed"], "vgg16.pb")
+```
+
+### 步骤三 模型转换
+
+```
+git clone https://github.com/PaddlePaddle/X2Paddle.git
+cd X2Paddle
+git checkout develop
+export PYTHONPATH=${PWD}
+mkdir paddle_model
+python x2paddle/convert.py --framework=tensorflow --model=x2paddle/tests/vgg16.pb --save_dir=paddle_model
+```