Clear and evolving contribution process & issue submission documentation

[LexiNadolski]

Context

For CNCF graduation, Flatcar must demonstrate:

• A clearly defined and easily discoverable process for submitting issues and changes (bugs, features, PRs).
• Comprehensive contributor documentation, with increasing detail and clarity as the project matures.

Currently, the main contribution and issue submission processes are documented in CONTRIBUTING.md and summarized in the README. The issue tracker and PR process are open and regularly reviewed. Ongoing efforts (#1817, #1791, #1816) further improve contributor onboarding, process documentation, and template clarity.

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Goals

• Ensure all users and contributors can easily find and understand how to submit issues, suggest changes, and contribute to Flatcar.
• Continuously improve and expand contributor documentation in line with project growth and community needs.

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Tasks / Next Steps

• Audit all entry points (README, CONTRIBUTING.md, website, docs) for clear, up-to-date, and prominent contribution and issue submission instructions.
• Cross-link documentation and templates for seamless navigation.
• Update documentation to reflect maturing processes (e.g., onboarding, code review, decision-making, roles).
• Collect and incorporate feedback from new and experienced contributors about the clarity and completeness of the process.
• Summarize improvements and evidence here for CNCF graduation review.

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References

• CONTRIBUTING.md
• Flatcar Issues
• README - Report Bugs & Request Features
• Graduation Tracker
• #1817
• #1791
• #1816