Document how to load the CVMFS environment

[ickc]

Everything is ready except to

• [ ] document it,
  • [ ] what would be a good user experience here? Wrapper scripts?
  • [ ] think about constraining to x86-64-v4
• [ ] think about long term support policy, we shouldn't be keeping all of them forever...

(base) [northgridsgm@cvmfs-uploader02 simonsobservatory]$ pwd
/cvmfs/northgrid.gridpp.ac.uk/simonsobservatory
(base) [northgridsgm@cvmfs-uploader02 simonsobservatory]$ ls -1 pmpm conda
conda:
so-conda-20231121
so-conda-20231122
so-conda-20231123
so-conda-py310-20231211
so-conda-py310-20231212
so-conda-py38-20231211
so-conda-py39-20231211

pmpm:
so-pmpm-py310-mkl-x86-64-v3-mpich-20231212
so-pmpm-py310-mkl-x86-64-v3-openmpi-20231212
so-pmpm-py310-mkl-x86-64-v4-mpich-20231212
so-pmpm-py310-mkl-x86-64-v4-openmpi-20231212
so-pmpm-py310-nomkl-x86-64-v3-mpich-20231212
so-pmpm-py310-nomkl-x86-64-v3-openmpi-20231212
so-pmpm-py310-nomkl-x86-64-v4-mpich-20231212
so-pmpm-py310-nomkl-x86-64-v4-openmpi-20231212

[ickc]

Close with 8050b21, 38afe07, 13e441e among others.