Docs: clarify language/runtime support matrix for contributors

[Vaishnav88sk]

Problem

Current contributor onboarding can be clearer regarding supported Python versions, R scope, and what CI actually validates.

Proposal

Add or update contributor documentation with a compact support matrix covering:

• Supported Python versions
• R component scope / supported environments
• What combinations are validated in CI
• Recommended local test commands by area (Python, R, docs, etc.)

Also clarify which checks are required before submitting changes versus optional deeper validation.

Acceptance criteria

• One canonical documentation section for the support matrix
• Clear distinction between required vs optional local checks
• Linked from CONTRIBUTING.md

Contribution

I’d be happy to work on this issue and contribute a PR if this approach sounds good.

[AshishPadala]

Hello, I'd like to help with this problem.

I applied for GSoC 2026 and recently set up Metaflow on my own computer using WSL (Ubuntu). I went through the onboarding process and ran the tutorial flows. While doing this, I saw that it would be easier for new contributors to understand things like Python version support, CI validation, and local testing expectations.

I'd be happy to suggest a structured support matrix and update the contributor documentation to reflect that. If you have any specific sections or formats in mind, please let me know.

Thank you!