Update README.md

TensorFlow2Paddle/README.md

 Warning: TensorFlow2Paddle is not stable yet
+
+Demo: How to change tensorflow resnet_v1_50 pretrained model to PaddlePaddle model for inference
+1. Get pretrained_model
+
+```
+git clone https://github.com/PaddlePaddle/X2Paddle.git
+cd X2Paddle/TensorFlow2Paddle
+wget http://download.tensorflow.org/models/resnet_v1_50_2016_08_28.tar.gz
+tar xzvf resnet_v2_50_2017_04_14.tar.gz
+```
+
+2. Change model to ckpt model with meta file
+
+
+```
+python demo/save_resnet_ckpt_model.py resnet_v1_50.ckpt ./new_ckpt_model
+```
+
+3. Export PaddlePaddle model
+
+```
+python demo/export_resnet_to_paddle_model.py new_ckpt_model/resnet.meta new_ckpt_model fluid_model
+```
+
+4. Test PaddlePaddle model
+```python 
+from fluid_model.mymodel import KitModel
+import paddle.fluid as fluid
+import numpy
+import os
+
+result = KitModel()
+exe = fluid.Executor(fluid.CPUPlace())
+exe.run(fluid.default_startup_program())
+
+var_list = list()
+for f in os.listdir('./fluid_model'):
+    f = f.split('/fluid')[-1]
+    if f.startswith("param_"):
+        var_list.append(fluid.default_main_program().global_block().var(f))
+fluid.io.load_vars(exe, './fluid', vars=var_list)
+
+test_data = numpy.random.rand(1, 3, 224, 224)
+test_data = numpy.array(test_data, dtype='float32')
+result = exe.run(fluid.default_main_program(), 
+      feed={'input_0':numpy.array(img_data, dtype='float32')}, 
+      fetch_list=[result])
+print(result)
+```