Fix documentation for setting TORCH_CUDA_ARCH_LIST

[matthewdcong]

1. Quotes are required for the TORCH_CUDA_ARCH_LIST so bash doesn't only pick up the first arch. Add that to the -h printout for ./build.sh.
2. Update the README to use --cuda-arch-list instead of setting TORCH_CUDA_ARCH_LIST.

[harrism]

Thanks for the fix! If it's not hard, it might also be good to support the ENV variable. That way one can set it in their shell so it can be reused.

[matthewdcong]

Thanks! I added support for the environment variable:

./build.sh install -v --cuda-arch-list="8.0;9.0"
Using specified TORCH_CUDA_ARCH_LIST=8.0;9.0

./build.sh install -v
Detecting CUDA architectures via nvidia-smi
Detected CUDA architectures: 12.0+PTX

TORCH_CUDA_ARCH_LIST="8.0;9.0" ./build.sh install -v
Using environment TORCH_CUDA_ARCH_LIST=8.0;9.0