Update installation description

[jgrooss]

It took me a while to get the setup. Maybe the description should be updated
or replaced by somethng else, e.g. pixi.

Details:
I used miniforge and a mamba environment

numpy < 2:
works only with older python version
mamba install 'python < 3.13'
mamba install 'numpy <2'

the following needed to be installed manually in environment, for some reason they
were not installed by using requirements.txtm maybe as a consequence of the numpy problem

python-eccodes
xarray
metPy
netCDF4