write documentation for installing a compatible version of pytorch and cuda

We have decided to leave installing compatible pytorch and cuda version up to the user. We should provide detailed information on
starting an environment, installing napari and our plugin, and installing a gpu version of pytorch (and cuda drivers, if needed) to the user.

For reference, here is how cellpose does this: https://github.com/MouseLand/cellpose?tab=readme-ov-file#gpu-version-cuda-on-windows-or-linux