(Re-re-re) Fix Conda MacOS ARM Installation Instructions

[michaelweinold]

Following the current documentation:

conda create -n brightway -c conda-forge -c cmutel brightway25_nosolver scikit-umfpack

to install Brightway on MacOS ARM (Apple Silicon) machines still results in the scikit-umfpack error on first package import:

[/opt/homebrew/Caskroom/miniconda/base/envs/bw25_arm/lib/python3.11/site-packages/bw2calc/__init__.py:45](https://file+.vscode-resource.vscode-cdn.net/opt/homebrew/Caskroom/miniconda/base/envs/bw25_arm/lib/python3.11/site-packages/bw2calc/__init__.py:45): UserWarning: 
It seems like you have an ARM architecture, but haven't installed scikit-umfpack:

    https://pypi.org/project/scikit-umfpack/

Installing it could give you much faster calculations.

  warnings.warn(UMFPACK_WARNING)