Tracking the codex sample config in Git

[hellodword]

The upstream example is published on the docs site, which makes change tracking awkward. Keeping a copy here makes it easy to review diffs, inspect history, and reference older versions when the example changes.

• https://github.com/hellodword/codex-example-config/blob/master/config.toml
• https://github.com/hellodword/codex-example-config/blob/master/config.generated.toml