Update readme with cu124 version

ghstack-source-id: 6eb7a87df8b3585e53993684d0b9682aeb99cfe5
Pull Request resolved: #719

README.md

@@ -73,7 +73,7 @@ We report our [Performance](docs/performance.md) verified on 64/128 GPUs.
 git clone https://github.com/pytorch/torchtitan
 cd torchtitan
 pip install -r requirements.txt
-pip3 install --pre torch --index-url https://download.pytorch.org/whl/nightly/cu121 --force-reinstall # or cu118
+pip3 install --pre torch --index-url https://download.pytorch.org/whl/nightly/cu124 --force-reinstall
 ```
 
 ### Downloading a tokenizer