[README] Add instructions to build torch for Blackwell (#5727)

Author: peterbell10

README.md

@@ -22,34 +22,68 @@ You can install the latest stable release of Triton from pip:
 pip install triton
 ```
 
-Binary wheels are available for CPython 3.8-3.12 and PyPy 3.8-3.9.
+Binary wheels are available for CPython 3.9-3.13.
 
-And the latest nightly release:
+# Enabling Blackwell Support
 
-```shell
-pip install -U --index-url https://aiinfra.pkgs.visualstudio.com/PublicPackages/_packaging/Triton-Nightly/pypi/simple/ triton-nightly
+The main branch now features support for NVIDIA Blackwell GPUs using 5th
+generation tensor cores. To enable this, you will need two additional steps:
+
+1. Build a pre-release PyTorch from source with CUDA 12.8
+2. Build triton from the latest source
+
+
+First, to build pytorch you need to have CUDA 12.8 installed locally. If not,
+follow the [instructions for your platform](https://developer.nvidia.com/cuda-downloads)
+```bash
+# Clone and checkout pytorch 2.6 release candidate
+git clone https://github.com/pytorch/pytorch
+cd pytorch
+git checkout v2.6.0-rc9
+git submodule sync
+git submodule update --init --recursive -j 8
+
+# Install build dependencies (assumes you already have a system compiler)
+pip install -r requirements.txt
+pip install mkl-static mkl-include wheel
+
+# Build PyTorch (will take a long time)
+export CUDA_HOME=/usr/local/cuda-12.8
+export CUDA_PATH=$CUDA_HOME
+export TORCH_CUDA_ARCH_LIST=Blackwell
+python setup.py develop
+
+# Optional, package build into a wheel to install on other machines.
+python setup.py bdist_wheel
+ls dist  # Wheel should be output in this directory
 ```
 
+Note that if you use the domain libraries (`torchvision`, `torchtext`,
+`torchaudio`, etc.) these will need to be built from source as well, otherwise
+their custom PyTorch extensions will not work.
+
+Finally, follow the instructions below to install triton from source.
+
 # Install from source
 
 ```shell
-git clone https://github.com/triton-lang/triton.git;
-cd triton;
+git clone https://github.com/triton-lang/triton.git
+cd triton
 
-pip install ninja cmake wheel pybind11; # build-time dependencies
+pip install ninja cmake wheel pybind11 # build-time dependencies
 pip install -e python
 ```
 
 Or with a virtualenv:
 
 ```shell
-git clone https://github.com/triton-lang/triton.git;
-cd triton;
+git clone https://github.com/triton-lang/triton.git
+cd triton
 
-python -m venv .venv --prompt triton;
-source .venv/bin/activate;
+python -m venv .venv --prompt triton
+source .venv/bin/activate
 
-pip install ninja cmake wheel pybind11; # build-time dependencies
+pip install ninja cmake wheel pybind11 # build-time dependencies
 pip install -e python
 ```