Add CONTRIBUTING.md with project standards and guidelines

[gwtaylor]

Summary

Adds a comprehensive CONTRIBUTING.md file to document project-specific standards and guidelines that have been identified through PR reviews, particularly during the FAIR Guide implementation in #37.

Changes

• Project Standards Documentation: Documents markdown formatting requirements, license format specifications, and technical constraints
• Development Workflow: Includes local setup, testing procedures, and quality assurance guidelines
• Commit Guidelines: Adopts conventional commits standard with project-specific examples
• Platform-Specific Requirements: Documents Hugging Face YAML formatting and MkDocs/Python-Markdown compatibility issues

Key Standards Documented

Markdown Formatting

• 4-space indentation for nested lists (due to Python-Markdown/MkDocs compatibility)
• Markdownlint configuration rationale
• Formatting consistency requirements

License Requirements

• Lowercase license identifiers in YAML frontmatter (cc0-1.0 not CC0-1.0) for Hugging Face compatibility
• Platform-specific formatting requirements

Development Process

• Local testing with mkdocs serve
• Quality assurance procedures
• PR submission guidelines

File Placement Decision

The file is placed in the repository root (not in docs/) to leverage GitHub's automatic detection and integration features for contributing guidelines. This follows standard GitHub conventions while noting that we considered placing it in docs/ for consistency with our existing documentation structure.

Testing

• File renders correctly in GitHub
• Local MkDocs build still works (mkdocs serve)
• All links are functional
• Markdown formatting follows project standards

Resolves #55

Test Plan

• @egrace479 and @hlapp review content for accuracy and completeness
• Verify all documented standards reflect current project practices
• Confirm the conventional commits format works for our workflow
• Consider if README.md should reference this file

🤖 Generated with Claude Code

[hlapp]

As per online discussion, changed back to draft stage to indicate that more changes are in the works already. Please change back to ready for review once those are in.

[hlapp]

Up to here content looks great, many thanks @gwtaylor for your work on this and @egrace479 for comments!

[gwtaylor]

@egrace479 I flagged you to have a check of the commit that implements the dev branch and Collaborative Distributed Science Guide retarget. If you're happy with that, this should be good to merge.

[egrace479]

This looks great! Just one small change to add the article in the title (as it is there throughout). Approving with this single change request.