add PYTHONPATH

tutorials/source_en/advanced_use/serving.md

@@ -61,6 +61,8 @@ If the server prints the `MS Serving Listening on 0.0.0.0:5500` log, the Serving
 
 ### Client Samples
 #### <span name="python-client-sample">Python Client Sample</span>
+ > Before running the client sample, add the path `/{your python path}/lib/python3.7/site-packages/mindspore/` to the environment variable `PYTHONPATH`.
+
 Obtain [ms_client.py](https://gitee.com/mindspore/mindspore/blob/master/serving/example/python_client/ms_client.py) and start the Python client.
 ```bash
 python ms_client.py

tutorials/source_zh_cn/advanced_use/serving.md

@@ -65,6 +65,8 @@ ms_serving --model_path={model directory} --model_name=tensor_add.mindir
 
 ### gRPC客户端示例
 #### <span name="python客户端示例">Python客户端示例</span>
+ > 执行客户端前，需将`/{your python path}/lib/python3.7/site-packages/mindspore`对应的路径加入到环境变量PYTHONPATH中。
+
 获取[ms_client.py](https://gitee.com/mindspore/mindspore/blob/master/serving/example/python_client/ms_client.py)，启动Python客户端。
 ```bash
 python ms_client.py