[Serving] Add a simple Python serving (#962)

* init simple serving

* simple serving is working

* ppyoloe demo

* Update README_CN.md

* update readme

* complete vision result to json

examples/vision/detection/paddledetection/python/serving/README_CN.md

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+简体中文 | [English](README_EN.md)
+
+# PaddleDetection Python轻量服务化部署示例
+
+在部署前，需确认以下两个步骤
+
+- 1. 软硬件环境满足要求，参考[FastDeploy环境要求](../../../../../../docs/cn/build_and_install/download_prebuilt_libraries.md)  
+- 2. FastDeploy Python whl包安装，参考[FastDeploy Python安装](../../../../../../docs/cn/build_and_install/download_prebuilt_libraries.md)
+
+服务端：
+```bash
+# 下载部署示例代码
+git clone https://github.com/PaddlePaddle/FastDeploy.git
+cd FastDeploy/examples/vision/detection/paddledetection/python/serving
+
+# 下载PPYOLOE模型文件（如果不下载，代码里会自动从hub下载）
+wget https://bj.bcebos.com/paddlehub/fastdeploy/ppyoloe_crn_l_300e_coco.tgz
+tar xvf ppyoloe_crn_l_300e_coco.tgz
+
+# 安装uvicorn
+pip install uvicorn
+
+# 启动服务，可选择是否使用GPU和TensorRT，可根据uvicorn --help配置IP、端口号等
+# CPU
+MODEL_DIR=ppyoloe_crn_l_300e_coco DEVICE=cpu uvicorn server:app
+# GPU
+MODEL_DIR=ppyoloe_crn_l_300e_coco DEVICE=gpu uvicorn server:app
+# GPU上使用TensorRT （注意：TensorRT推理第一次运行，有序列化模型的操作，有一定耗时，需要耐心等待）
+MODEL_DIR=ppyoloe_crn_l_300e_coco DEVICE=gpu USE_TRT=true uvicorn server:app
+```
+
+客户端：
+```bash
+# 下载部署示例代码
+git clone https://github.com/PaddlePaddle/FastDeploy.git
+cd FastDeploy/examples/vision/detection/paddledetection/python/serving
+
+# 下载测试图片
+wget https://gitee.com/paddlepaddle/PaddleDetection/raw/release/2.4/demo/000000014439.jpg
+
+# 请求服务，获取推理结果（如有必要，请修改脚本中的IP和端口号）
+python client.py
+```