Created by: jeng1220

The prebuilt PaddlePaddle package is built without TensorRT support (via pip or docker), so the user who want to use Paddle-TensorRT must build from source by themselves. However, there is NO statement regarding -DTENSORRT_ROOT=${TensorRT_ROOT_DIR} in latest PaddlePaddle document, such as paddle_tensorrt_infer.md and python_infer_cn.md, so user are unable to know how to build Paddle-TensorRT correctly.