Add GitHub Actions workflow for documentation deployment

[xtian15]

Summary

• Add GitHub Actions workflow to build and deploy documentation to GitHub Pages
• Update documentation copyright/authorship to reflect NOAA-GFDL ownership
• Enables GFDL team to maintain documentation without external dependencies

Background

Issue #67 identified that Pace documentation is currently hosted at ai2cm.github.io/pace/, which is controlled by AI2 and cannot be edited by the GFDL team. This PR migrates documentation hosting to the NOAA-GFDL repository's own GitHub Pages.

Changes

1. New file: .github/workflows/docs.yml

GitHub Actions workflow that:

• Triggers on push to main/develop branches
• Builds Sphinx documentation using existing docs/ configuration
• Deploys to GitHub Pages on the NOAA-GFDL repository
• Runs on PRs (build only, no deploy) for validation

2. Modified: docs/conf.py

Updated project metadata:

# Before
copyright = "2022, AI2 Climate Modeling Team"
author = "AI2 Climate Modeling Team"

# After
copyright = "2022-2025, NOAA-GFDL (originally developed by AI2 Climate Modeling Team)"
author = "NOAA-GFDL"

Post-Merge Setup Required

After merging, a repository admin needs to:

1. Go to Settings → Pages
2. Set Source to "GitHub Actions"
3. Documentation will then be available at noaa-gfdl.github.io/Pace/

Test Plan

• Sphinx build succeeds locally (cd docs && make html)
• Build produces 17 HTML pages with no errors
• Copyright reflects NOAA-GFDL in generated HTML
• GitHub Actions workflow runs successfully (verify after push)
• Documentation accessible at new URL (verify after Pages setup)

Impact

• No breaking changes to existing functionality
• Backward compatible - existing RTD config preserved for reference
• Enables community contributions to documentation
• Removes dependency on external AI2 infrastructure

Fixes #67