README says "zero dependencies" but npm installs prop-types

### Summary

The README describes react-tiny-virtual-list as having **"zero dependencies"** (and "dependency free"),
but the published npm package installs `prop-types`. A small inconsistency — raising it kindly in case
the wording or the packaging wants a tweak.

### What the README says

- "> A tiny but mighty list virtualization library, **with zero dependencies** 💪"
- "**Tiny & dependency free** – Only 3kb gzipped"
- "…a tiny, lightweight and **dependency-free** list virtualization library…"

### What npm actually installs (observation)

`react-tiny-virtual-list` (latest) declares:

```json
"dependencies": { "prop-types": "^15.5.7" }
```

(verified at `registry.npmjs.org/react-tiny-virtual-list/latest`.) So `npm install
react-tiny-virtual-list` also pulls `prop-types`.

### Possible directions (your call)

- If `prop-types` is only used for dev-time validation, it could move to `devDependencies` /
`peerDependencies` so the "zero dependencies" claim holds, **or**
- Update the README to note the single `prop-types` dependency.

Happy to send a small PR either way. Thanks for the library — the API is lovely!

_{AI-assisted; I verified the npm registry metadata and the README myself against commit `bf907992f1f1`.}

Start with the README claims and compare them with the published package metadata at registry.npmjs.org, including the prop-types dependency. Determine whether the project should change the wording or adjust packaging, then verify that the README and npm install behavior consistently describe the dependency situation.

Written by the indexing model from the issue text.