Minor grammar cleanup in codex-rs README

Question

### What is the type of issue?

Documentation is incorrect

### What is the issue?

I noticed a small grammar issue in `codex-rs/README.md` under “Code Organization”.

Current wording:

> Ultimately, we hope this to be a library crate that is generally useful for building other Rust/native applications that use Codex.

Suggested wording:

> Ultimately, we hope this becomes a library crate that is generally useful for building other Rust/native applications that use Codex.

I have a one-line bran