README / docs refactor (#2724)

This PR cleans up the monolithic README by breaking it into a set
navigable pages under docs/ (install, getting started, configuration,
authentication, sandboxing and approvals, platform details, FAQ, ZDR,
contributing, license). The top‑level README is now more concise and
intuitive, (with corrected screenshots).

It also consolidates overlapping content from codex-rs/README.md into
the top‑level docs and updates links accordingly. The codex-rs README
remains in place for now as a pointer and for continuity.

Finally, added an extensive config reference table at the bottom of
docs/config.md.

---------

Co-authored-by: easong-openai <easong@openai.com>

docs/faq.md

@@ -0,0 +1,23 @@
+## FAQ
+
+### OpenAI released a model called Codex in 2021 - is this related?
+
+In 2021, OpenAI released Codex, an AI system designed to generate code from natural language prompts. That original Codex model was deprecated as of March 2023 and is separate from the CLI tool.
+
+### Which models are supported?
+
+We recommend using Codex with GPT-5, our best coding model. The default reasoning level is medium, and you can upgrade to high for complex tasks with the `/model` command.
+
+You can also use older models by using API-based auth and launching codex with the `--model` flag.
+
+### Why does `o3` or `o4-mini` not work for me?
+
+It's possible that your [API account needs to be verified](https://help.openai.com/en/articles/10910291-api-organization-verification) in order to start streaming responses and seeing chain of thought summaries from the API. If you're still running into issues, please let us know!
+
+### How do I stop Codex from editing my files?
+
+By default, Codex can modify files in your current working directory (Auto mode). To prevent edits, run `codex` in read-only mode with the CLI flag `--sandbox read-only`. Alternatively, you can change the approval level mid-conversation with `/approvals`.
+
+### Does it work on Windows?
+
+Running Codex directly on Windows may work, but is not officially supported. We recommend using [Windows Subsystem for Linux (WSL2)](https://learn.microsoft.com/en-us/windows/wsl/install).