change readme install instructions

[PhiSpel]

Description

• updated requirements to be used directly in PyCharm or conda
• updated Readme
• Note: approximate package requirements (~=) are not recognized by Conda
• Note for Readme: one may need to manually specify the CUDA_HOME variable for native (to the package folder .../cudatoolkit_* containing /bin/nvcc)

closes #170
closes #234

Checklist

• This pull request is associated to an issue
• This PR contains a description
• Add someone else as reviewer and wait for approval before merging.

[PhiSpel]

my best bet for installation:

git clone https://github.com/lettucecfd/lettuce.git lettuce
cd lettuce
conda update conda
conda create -n lettuce
conda activate lettuce
...check CUDA version
conda install pytorch>=2.4 pytorch-cuda=12.1 -c pytorch -c nvidia
conda install --file requirements.txt -c pytorch -c nvidia -c conda-forge
...maybe set CUDA_HOME variable
python setup.py develop
lettuce convergence
pytest tests

for now:

git clone https://github.com/lettucecfd/lettuce.git lettucetest
cd lettucetest
git fetch origin
git checkout 234-feature-change-readme-install-instructions
conda create --yes -n lettucetest
conda activate lettucetest
conda install --yes pytorch>=2.4 pytorch-cuda=12.1 -c pytorch -c nvidia
conda install --yes --file requirements.txt -c pytorch -c nvidia -c conda-forge
pip install -e setup.py
lettuce convergence
pytest tests

to tidy up:

cd ..
rm -r lettucetest
conda deactivate
conda remove -n lettucetest --all --yes

[PhiSpel]

@McBs

• do we need exact restricitons for packaging, click and setuptools?
• can you check if the instructions above or, ideally, in the new readme work for you?

[McBs]

@McBs

* [x]  do we need exact restricitons for `packaging`, `click` and `setuptools`?

* [x]  can you check if the instructions above or, ideally, in the new readme work for you?

Hi @PhiSpel
the instructions work on my workstation :-)

[McBs]

lgtm