Update README.md: add NASA GMAO

[climbfuji]

Description

When we added NASA GMAO as a project partner, we update project-charter.md, but forgot about README.md. This PR fixes the oversight.

Dependencies

n/a

Issues addressed

n/a

Applications affected

n/a

Systems affected

n/a

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