Updating Codex Contribution Guidelines

Peak irony: OpenAI's Codex project is being DDoS'd by its own creation.

They made code generation essentially free, and now they're drowning in AI-generated PRs that take more time to review than it would take to just write the fix themselves. So they've moved to invitation-only contributions. They built the tools that removed code as a barrier, and now they're living with what that actually means: quantity goes up, quality goes down, and every PR still needs a human with architectural context to evaluate it.

The bottleneck has completely flipped. It used to be finding someone to write the code. Now anyone can dump a 200-line PR in seconds, but the review time from someone who actually understands the codebase is the most expensive thing in the repo. That context can't be generated, it has to be earned.

They built a firehose and their own team can't drink from it.