update pip to pip3

doc/doc_ch/whl.md

@@ -12,7 +12,7 @@ pip install paddleocr
 本地构建并安装
 ```bash
 python3 setup.py bdist_wheel
-pip install dist/paddleocr-x.x.x-py3-none-any.whl # x.x.x是paddleocr的版本号
+pip3 install dist/paddleocr-x.x.x-py3-none-any.whl # x.x.x是paddleocr的版本号
 ```
 ### 1. 代码使用
 

doc/doc_en/whl_en.md

@@ -10,7 +10,7 @@ pip install paddleocr
 build own whl package and install
 ```bash
 python3 setup.py bdist_wheel
-pip install dist/paddleocr-x.x.x-py3-none-any.whl # x.x.x is the version of paddleocr
+pip3 install dist/paddleocr-x.x.x-py3-none-any.whl # x.x.x is the version of paddleocr
 ```
 ### 1. Use by code