Add detailed CUDA installation note for gpu installation

install/mindspore_gpu_install.md

@@ -32,6 +32,7 @@
 
 - 在联网状态下，安装whl包时会自动下载`requirements.txt`中的依赖项，其余情况需自行安装。
 - 为了方便用户使用，MindSpore降低了对Autoconf、Libtool、Automake版本的依赖，可以使用系统自带版本。
+- CUDA安装后，需要设置环境变量`PATH`（如：`export PATH=/usr/local/cuda-${version}/bin:$PATH`）和`LD_LIBRARY_PATH`（如：`export LD_LIBRARY_PATH=/usr/local/cuda-${version}/lib64:$LD_LIBRARY_PATH`），详细安装后的设置可参考[CUDA安装手册](https://docs.nvidia.com/cuda/cuda-installation-guide-linux/index.html#post-installation-actions)。
 
 ### Conda安装（可选）
 

install/mindspore_gpu_install_en.md

@@ -32,6 +32,7 @@ This document describes how to quickly install MindSpore in a NVIDIA GPU environ
 
 - When the network is connected, dependency items in the `requirements.txt` file are automatically downloaded during `.whl` package installation. In other cases, you need to manually install dependency items.
 - MindSpore reduces dependency on Autoconf, Libtool, Automake versions for the convenience of users, default versions of these tools built in their systems are now supported.
+- After installing CUDA, environment variable `PATH`(e.g. `export PATH=/usr/local/cuda-${version}/bin:$PATH`) and `LD_LIBRARY_PATH`(e.g. `export LD_LIBRARY_PATH=/usr/local/cuda-${version}/lib64:$LD_LIBRARY_PATH`) need to be set. Please refer to [CUDA installation guide](https://docs.nvidia.com/cuda/cuda-installation-guide-linux/index.html#post-installation-actions) for detailed post installation actions.
 
 ### (Optional) Installing Conda