Update readme for use with GPU

[DerkKooi]

No description provided.

[Copilot]

Pull request overview

This pull request updates the GPU installation instructions for Skala, adding support for both CUDA 12 and CUDA 13 environments.

Changes:

• Added two new conda environment files for GPU support (CUDA 12 and CUDA 13)
• Updated README.md with comprehensive GPU installation instructions for both conda and pip
• Updated docs/installation.rst to reference the new environment files and provide CUDA 13 installation instructions

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 6 comments.

File	Description
environment-gpu_cu12.yml	New conda environment file for CUDA 12 GPU support with pytorch-gpu, cupy, and cuda toolkit dependencies
environment-gpu_cu13.yml	New conda environment file for CUDA 13 GPU support with pytorch-gpu, cupy, and cuda toolkit dependencies
docs/installation.rst	Updated installation documentation to reference new environment files and add CUDA 13 gpu4pyscf installation instructions
README.md	Added GPU installation section with conda and pip instructions for CUDA 12 and 13 support

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[awvwgk]

Do we have the possibility to stay with a single GPU environment? Maybe we can add in the instructions that it is necessary to update the Cuda version in the environment for Cuda 13 rather than providing two identical environments with one different version constraint.

Alternatively, could you check whether CONDA_OVERRIDE_CUDA still works for setting the Cuda version lower bound from the environment?

[awvwgk]

Looks good to me.