Document the use of miniconda

[adamltyson]

There are many issues about documenting the use of conda. I think this means we should actually do it.

• Add a how-to for setting up conda on windows. #44
• Write up a guide to miniconda - why you should use it, how to etc. #29
• Document how to set up conda/python etc on apple silicon #18

[adamltyson]

conda will be moving to the mamba solver so this means we should be able to just document miniconda and ignore the complexities of mamba et al.

[niksirbi]

We also discovered that creating a conda environment with the miniconda module during an interactive job (started via srun -p cpu --pty bash -i) is very slow. Creating the same environment on the gateway node seems to be faster. If confirmed, we should solve this or at least document it.