Add NCAR MMM as a project member, update README.md to point to Wiki

[climbfuji]

Description

This PR removes project_charter.md (now lives in the spack-stack wiki) and updates README.md to point directly to the spack-stack wiki to avoid duplication.

Alongside with this PR, I went through the Wiki and added NCAR MMM as a project member and site maintainer for the Derecho tier 1 system.

No need to run the tests for changes to these files.

Dependencies

n/a

Issues addressed

Housekeeping.

Applications affected

None

Systems affected

None

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 (spack-stack wiki) will be made when this PR is merged