Correct documentation for Hercules and Orion

[RatkoVasic-NOAA]

Correct documentation for Hercules and Orion changes in post-install edits of modulefiles.

Description

Loading spack-managed-x86-64_v3 module on Hercules and Orion messes up MODULEPATH, hence need for manual edits of modulefiles after spack-stack installation.

Dependencies

Issues addressed

No issue opened

Applications affected

Systems affected

Hercules and Orion documentation.

Testing

• CI: Note whether the automatic tests (GitHub actions tests that run automatically for every commit) pass or not
  • GitHub actions CI tests pass
  • GitHub actions CI tests do not pass (provide explanation)
  • GitHub actions CI tests skipped (provide explanation if necessary)
• New tests added: List and describe any new tests added to GitHub actions
  • ...
• Additional testing: Add information on any additional tests conducted
  • ...

Checklist

• This PR addresses one issue/problem/enhancement or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications.
• All dependency PRs/issues have been resolved and this PR can be merged.
• All necessary updates to the documentation on readthedocs are included in this PR
  • For site config updates, check in particular doc/source/PreConfiguredSites.rst and doc/source/MaintainersSection.rst
• All necessary updates to the spack-stack wiki will be made when this PR is merged

[climbfuji]

I'll defer to @rickgrubin-noaa for approving since I am not familiar with these manual post-install changes, and I no longer have access to Orion or Hercules.