Improve python installation with conda.

[DiamonDinoia]

While conda is not officially supported we should integrate @remy-abergel solution into our docs.

##################
# Clone the code #
##################
git clone https://github.com/flatironinstitute/finufft.git
cd finufft

####################################
# create a fresh conda environment #
####################################
conda update -y -n base -c defaults conda
conda create -y -n finufft-conda-no-binaries pip
conda activate finufft-conda-no-binaries

#######################
# Install (cu)FINUFFT #
#######################
conda install nvidia/label/cuda-12.4.0::cuda-toolkit
conda install conda-forge::fftw # needed for next step (finufft installation with pip), otherwise it fails
pip install --no-binary finufft python/finufft # success!
pip install --no-binary cufinufft python/cufinufft # success!

These installation instructions also worked on the other machine that I mentioned in my previous post (with Ubuntu 22.04 and two NVIDIA A40 GPUs). I think that using the NVIDIA repository (instead of conda-forge) for installing cudatoolkit is what solved the installation issues I was encountering before.

Originally posted by @remy-abergel in #649 (reply in thread)