fix doc

fix doc

python/examples/ocr/README.md

@@ -15,31 +15,6 @@ tar -xzvf ocr_det.tar.gz
 wget --no-check-certificate https://paddle-serving.bj.bcebos.com/ocr/test_imgs.tar
 tar xf test_imgs.tar
 ```
-## C++ OCR Service
-
-### Start Service
-Select a startup mode according to CPU / GPU device
-
-After the -- model parameter, the folder path of multiple model files is passed in to start the prediction service of multiple model concatenation.
-```
-#for cpu user
-python -m paddle_serving_server.serve --model ocr_det_model ocr_rec_model --port 9293
-#for gpu user
-python -m paddle_serving_server_gpu.serve --model ocr_det_model ocr_rec_model --port 9293 --gpu_id 0
-```
-
-### Client Prediction
-The pre-processing and post-processing is in the C + + server part, the image's Base64 encoded string is passed into the C + + server.
-
-so the value of parameter `feed_var` which is in the file `ocr_det_client/serving_client_conf.prototxt` should be changed.
-
-for this case, `feed_type` should be 3(which means the data type is string),`shape` should be 1.
-
-By passing in multiple client folder paths, the client can be started for multi model prediction.
-```
-python ocr_c_client_bytes.py ocr_det_client ocr_rec_client
-```
-
 
 ## Web Service
 
@@ -123,3 +98,30 @@ python rec_debugger_server.py gpu #for gpu user
 ```
 python rec_web_client.py
 ```
+
+## C++ OCR Service
+
+**Notice：** If you need to concatenate det model and rec model, and do pre-processing and post-processing in Paddle Serving C++ framework, you need to use the C++ server compiled with WITH_OPENCV option，see[COMPILE.md](../../../doc/COMPILE.md)
+
+### Start Service
+Select a startup mode according to CPU / GPU device
+
+After the -- model parameter, the folder path of multiple model files is passed in to start the prediction service of multiple model concatenation.
+```
+#for cpu user
+python -m paddle_serving_server.serve --model ocr_det_model ocr_rec_model --port 9293
+#for gpu user
+python -m paddle_serving_server_gpu.serve --model ocr_det_model ocr_rec_model --port 9293 --gpu_id 0
+```
+
+### Client Prediction
+The pre-processing and post-processing is in the C + + server part, the image's Base64 encoded string is passed into the C + + server.
+
+so the value of parameter `feed_var` which is in the file `ocr_det_client/serving_client_conf.prototxt` should be changed.
+
+for this case, `feed_type` should be 3(which means the data type is string),`shape` should be 1.
+
+By passing in multiple client folder paths, the client can be started for multi model prediction.
+```
+python ocr_c_client_bytes.py ocr_det_client ocr_rec_client
+```