Create README_CN.md

Add PPYOLO README_CN

python/examples/pipeline/PaddleDetection/ppyolo_mbv3/README_CN.md

+# PPYOLO model on Pipeline Paddle Serving
+
+(简体中文|[English](./README_CN.md))
+
+### 获取模型
+```
+wget --no-check-certificate https://paddle-serving.bj.bcebos.com/pddet_demo/2.0/ppyolo_mbv3_large_coco.tar
+```
+
+### 启动服务
+```
+tar xf ppyolo_mbv3_large_coco.tar
+python3 web_service.py
+```
+
+### 执行预测
+```
+python3 pipeline_http_client.py
+```