message: add C++ example in Model_Zoo
diff: @@ -10,6 +10,7 @@ Special thanks to the [Padddle wholechain](https://www.paddlepaddle.org.cn/whole
  | Model | Type | Framework | Download |
  | --- | --- | --- | ---- |
  +| pp_shitu | PaddleClas | [C++ Serving](../examples/C++/PaddleClas/pp_shitu) | [.tar.gz](https://paddle-imagenet-models-name.bj.bcebos.com/dygraph/rec/models/inference/serving/pp_shitu.tar.gz) |
  | resnet_v2_50_imagenet | PaddleClas | [C++ Serving](../examples/C++/PaddleClas/resnet_v2_50)</br>[Pipeline Serving](../examples/Pipeline/PaddleClas/ResNet_V2_50) | [.tar.gz](https://paddle-serving.bj.bcebos.com/paddle_hub_models/image/ImageClassification/resnet_v2_50_imagenet.tar.gz) | Pipeline Serving, C++ Serving|
  | mobilenet_v2_imagenet | PaddleClas | [C++ Serving](../examples/C++/PaddleClas/mobilenet) | [.tar.gz](https://paddle-serving.bj.bcebos.com/paddle_hub_models/image/ImageClassification/mobilenet_v2_imagenet.tar.gz) |
  | resnet50_vd | PaddleClas | [C++ Serving](../examples/C++/PaddleClas/imagenet)</br>[Pipeline Serving](../examples/Pipeline/PaddleClas/ResNet50_vd) | [.tar.gz](https://paddle-serving.bj.bcebos.com/model/ResNet50_vd.tar) |
  