docs: "Configuration" is not belongs "Getting started" (#4797)

I finished reading “Getting Started,” but couldn’t find the
“Configuration” section in the README. After following the link, I
realized “Configuration” is in a separate file, so I updated the README
accordingly.

# External (non-OpenAI) Pull Request Requirements

Before opening this Pull Request, please read the dedicated
"Contributing" markdown file or your PR may be closed:
https://github.com/openai/codex/blob/main/docs/contributing.md

If your PR conforms to our contribution guidelines, replace this text
with a detailed and high quality description of your changes.

Co-authored-by: Eric Traut <etraut@openai.com>

README.md

@@ -79,7 +79,7 @@ Codex CLI supports a rich set of configuration options, with preferences stored
   - [Example prompts](./docs/getting-started.md#example-prompts)
   - [Custom prompts](./docs/prompts.md)
   - [Memory with AGENTS.md](./docs/getting-started.md#memory-with-agentsmd)
-  - [Configuration](./docs/config.md)
+- [**Configuration**](./docs/config.md)
 - [**Sandbox & approvals**](./docs/sandbox.md)
 - [**Authentication**](./docs/authentication.md)
   - [Auth methods](./docs/authentication.md#forcing-a-specific-auth-method-advanced)