chore: new code of conduct draft; proposed language updates to README

[castastrophe]

Code of Conduct

• Add CODE_OF_CONDUCT.md based on Contributor Covenant v1.4
• Add a "Consequences" section outlining enforcement actions (correction, warning, temporary ban, permanent ban)

README improvements

• Suggest updates to grammar, punctuation, and sentence structure
• Strengthen language (e.g., "give you a leg up" → "provide a competitive advantage")
• Adjust heading hierarchy in FAQ
• Streamline redundant phrases and improve clarity
• Update intro text and section headers ("manifesto" → "guiding principles")

The goal of these changes was to improve clarity and professionalism while maintaining the original meaning.

[ljharb]

seems good, but should we base it on v2 or v3? v1.6 is pretty out of date.