Update docs for arm64

[robertdstein]

From working with LANL students installing NMMA on Macbooks, we found the following trick substantially simplified install/avoided the Arm 64 issues.

For either science user installation or developer installation, replace the line:

conda create --name nmma_env python=3.10

with:

conda create --name nmma_env
conda config --env --set subdir osx-64
conda install  python=3.10

The rest of the install steps should then proceed as normal.

[sahiljhawar]

@robertdstein A similar trick is done for tensorflow installation on arm mac (in the recently added build steps), I am yet to write documentation on this. By any chance is this also trying to simplify the tensorflow installation.

[robertdstein]

This solves problems for many packages (e.g PyFFTW) found using the standard installation process. We did not test it for tensorflow specifically, so I have no idea whether this simplifies tensorflow too.