README project tree lists missing integration/src/config.rs

The README's project tree lists `integration/src/config.rs`, but the current template does not include that file.

Current `integration/src` contents are:

```text
integration/src/
├── bin/increment_count.rs
├── helpers.rs
└── lib.rs
```

README currently shows:

```text
integration/
└── src/
├── bin/
├── config.rs # Temporary config file (do not modify!)
├── helpers.rs # Temporary helper file (do not modify!)
└── lib.rs
```

This makes the generated project structure look different from what users actually get after cloning/scaffolding the template. The fix should be small: remove the stale `config.rs` entry from the README tree.