Update README.md

Adding python 3.12 in document.
Adding more cuda version (cu121, cu122) in doc, with a method to detect the driver's cuda version (with nvidia-smi)
Provide a way to probe the most recent CUDA version that oneflow support.
Adding things related to PEP 668

README.md

@@ -24,7 +24,7 @@ OneFlow is a deep learning framework designed to be **user-friendly, scalable an
 
 ### General
 - Linux
-- Python 3.7, 3.8, 3.9, 3.10, 3.11
+- Python 3.7, 3.8, 3.9, 3.10, 3.11, 3.12
 
 ### CUDA
 - CUDA arch 60 or above
@@ -43,6 +43,33 @@ docker pull oneflowinc/oneflow:nightly-cuda11.8
 
 ### Pip Install
 
+- (*Optional*) Dealing with [PEP 668](https://peps.python.org/pep-0668/)
+ <details>
+ <summary>PEP 668 introduce marking installations as EXTERNALLY-MANAGED, which might stop you from installing packages.</summary>
+
+ When python code
+ ```python
+ __import__('os').path.exists(__import__('sysconfig').get_path('stdlib', __import__('sysconfig').get_default_scheme())+'/EXTERNALLY-MANAGED')
+ ```
+ returns `True`, python without a virtual environment is regarded as an `EXTERNALLY-MANAGED` installation.
+
+ In this case, `pip` cannot install any package directly since it will *break system packages*.
+
+ To bypass that issue, either install oneflow in a virtual environment created by
+ ```bash
+ python3 -m venv /path/to/venv
+ ```
+ then use `/path/to/venv/bin/python3` instead of `python3` to execute the following steps.
+
+ Adding a flag `--break-system-packages` after `pip install` to prove you know the consequene.
+
+ If you are boring with adding `--break-system-packages` flag, you could directly delete the file located at 
+ ```bash
+ python -c "print(__import__('sysconfig').get_path('stdlib', __import__('sysconfig').get_default_scheme())+'/EXTERNALLY-MANAGED')"
+ ```
+ (This operation usually needs root permission). After that, the python build no longer regarded as *EXTERNALLY-MANAGED* build, and you could directly execute commands below.
+</details>
+
 - (**Highly recommended**) Upgrade pip
 
  ```
@@ -66,7 +93,24 @@ docker pull oneflowinc/oneflow:nightly-cuda11.8
  ```bash
  python3 -m pip install --pre oneflow -f https://oneflow-staging.oss-cn-beijing.aliyuncs.com/branch/master/cu118
  ```
+ <details>
+ <summary>Here, `cu118` could be changed into other supported version (e.g., `cu121`, `cu122`).</summary>
+
+ The highest support cuda version could be obtained by
+ `nvidia-smi --version | grep CUDA`
+ (in case CUDA toolkit is installed).
+
+ Suppose you have `CUDA Version : 12.6`, you could use https://oneflow-staging.oss-cn-beijing.aliyuncs.com/branch/master/cu122.
 
+ You could try visiting
+ ```
+ https://oneflow-staging.oss-cn-beijing.aliyuncs.com/branch/master/cu126
+ https://oneflow-staging.oss-cn-beijing.aliyuncs.com/branch/master/cu127
+ ...
+ ```
+ to probe whether a new oneflow version is online.
+</details> 
+
  If you are in China, you could run this to have pip download packages from domestic mirror of pypi:
  ```
  python3 -m pip config set global.index-url https://pypi.tuna.tsinghua.edu.cn/simple