add faq

doc/doc_ch/FAQ.md

@@ -49,3 +49,5 @@ PaddleOCR已完成Windows和Mac系统适配，运行时注意两点：1、在[
 11. **自定义字典训练的模型，识别结果出现字典里没出现的字**  
 预测时没有设置采用的自定义字典路径。设置方法是在预测时，通过增加输入参数rec_char_dict_path来设置。
 
+12. **cpp infer与python inference的结果不一致，相差较大**  
+导出的inference model版本与预测库版本需要保持一致，比如在Windows下，Paddle官网提供的预测库版本是1.8，而PaddleOCR提供的inference model 版本是1.7，因此最终预测结果会有差别。可以在Paddle1.8环境下导出模型，再基于该模型进行预测。

doc/doc_en/FAQ_en.md

@@ -49,5 +49,8 @@ Error message: Input(X) dims[3] and Input(Grid) dims[2] should be equal, but rec
 Solution：TPS does not support variable shape. Please set --rec_image_shape='3,32,100' and --rec_char_type='en'
 
 11. **Custom dictionary used during training, the recognition results show that words do not appear in the dictionary**  
-
 The used custom dictionary path is not set when making prediction. The solution is setting parameter `rec_char_dict_path` to the corresponding dictionary file.
+
+
+12. **Results of cpp_infer and python_inference are very different**  
+Versions of exprted inference model and inference libraray should be same. For example, on Windows platform, version of the inference libraray that PaddlePaddle provides is 1.8, but version of the inference model that PaddleOCR provides is 1.7, you should export model yourself(`tools/export_model.py`) on PaddlePaddle1.8 and then use the exported model for inference.