[doc] updated readme regarding pypi installation (#2406)

README-zh-Hans.md

@@ -255,6 +255,28 @@ Colossal-AI 为您提供了一系列并行组件。我们的目标是让您的
 
 ## 安装
 
+### 从PyPI安装
+
+您可以用下面的命令直接从PyPI上下载并安装Colossal-AI。我们默认不会安装PyTorch扩展包
+
+```bash
+pip install colossalai
+```
+
+但是，如果你想在安装时就直接构建PyTorch扩展，您可以设置环境变量`CUDA_EXT=1`.
+
+```bash
+CUDA_EXT=1 pip install colossalai
+```
+
+**否则，PyTorch扩展只会在你实际需要使用他们时在运行时里被构建。**
+
+与此同时，我们也每周定时发布Nightly版本，这能让你提前体验到新的feature和bug fix。你可以通过以下命令安装Nightly版本。
+
+```bash
+pip install colossalai-nightly
+```
+
 ### 从官方安装
 
 您可以访问我们[下载](https://www.colossalai.org/download)页面来安装Colossal-AI，在这个页面上发布的版本都预编译了CUDA扩展。
@@ -274,10 +296,10 @@ pip install -r requirements/requirements.txt
 pip install .
 ```
 
-如果您不想安装和启用 CUDA 内核融合（使用融合优化器时强制安装）：
+我们默认在`pip install`时不安装PyTorch扩展，而是在运行时临时编译，如果你想要提前安装这些扩展的话（在使用融合优化器时会用到），可以使用一下命令。
 
 ```shell
-NO_CUDA_EXT=1 pip install .
+CUDA_EXT=1 pip install .
 ```
 
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README.md

@@ -257,9 +257,32 @@ Acceleration of [AlphaFold Protein Structure](https://alphafold.ebi.ac.uk/)
 
 ## Installation
 
+### Install from PyPI
+
+You can easily install Colossal-AI with the following command. **By defualt, we do not build PyTorch extensions during installation.**
+
+```bash
+pip install colossalai
+```
+
+However, if you want to build the PyTorch extensions during installation, you can set `CUDA_EXT=1`.
+
+```bash
+CUDA_EXT=1 pip install colossalai
+```
+
+**Otherwise, CUDA kernels will be built during runtime when you actually need it.**
+
+We also keep release the nightly version to PyPI on a weekly basis. This allows you to access the unreleased features and bug fixes in the main branch.
+Installation can be made via
+
+```bash
+pip install colossalai-nightly
+```
+
 ### Download From Official Releases
 
-You can visit the [Download](https://www.colossalai.org/download) page to download Colossal-AI with pre-built CUDA extensions.
+You can visit the [Download](https://www.colossalai.org/download) page to download Colossal-AI with pre-built PyTorch extensions.
 
 
 ### Download From Source
@@ -270,9 +293,6 @@ You can visit the [Download](https://www.colossalai.org/download) page to downlo
 git clone https://github.com/hpcaitech/ColossalAI.git
 cd ColossalAI
 
-# install dependency
-pip install -r requirements/requirements.txt
-
 # install colossalai
 pip install .
 ```