Add installation help for ARM / Apple silicon macs

[corneliusroemer]

I managed to install pangolin natively using this script - the standard one doesn't work

conda create -n pangolin
conda activate pangolin
conda config --env --add channels defaults
conda config --env --add channels bioconda
conda config --env --add channels conda-forge
conda config --env --set channel_priority strict
conda config --env --set subdir osx-64
mamba install pangolin #or conda if mamba is not installed