README manual release install docs point to single-binary archives instead of package archives

What happened?

The README's manual GitHub Release install section tells users to download single-binary archives such as:

• codex-aarch64-apple-darwin.tar.gz
• codex-x86_64-apple-darwin.tar.gz
• codex-x86_64-unknown-linux-musl.tar.gz
• codex-aarch64-unknown-linux-musl.tar.gz

and then rename the extracted binary to codex.

Current releases also publish codex-package-<target>.tar.gz archives, and the install scripts prefer the package layout. The package archives include the expected directory layout such as bin/codex, vendored tools/resources, and package metadata, while the README points users to the older single-binary layout.

Expected behavior

The manual release install docs should either point users to the canonical codex-package-<target>.tar.gz archives or explain when users should choose the single-binary archives versus the package archives.

Additional context

I searched open issues and PRs for terms including README manual GitHub Release install, codex-package, archive install, and single-binary archives, and did not find an existing open item that appears to cover this docs mismatch.