message: add doc for ocr
diff: @@ -15,6 +15,29 @@ 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
  