Document the MPI settings for each machine/job

[DavidHuber-NOAA]

What new functionality do you need?

There are multiple locations in the env files that MPI settings are set but not documented. These need to be documented -- both their purpose and why they are needed -- so that

1. we understand their use, who recommended them, and why to reduce guess work/research
2. when new, similar systems are brought online we have a better idea of what settings should be on/off
3. if there is an upgrade to MPI, these settings can be easily checked to determine if they will still be needed

What are the requirements for the new functionality?

Each MPI setting is documented with 1) what does it do, 2) who recommended it, and 3) why is it needed.

Acceptance Criteria

All MPI settings are documented for each machine.

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