Docs: useReactor is undocumented
[`useReactor`](https://github.com/tldraw/tldraw/blob/fae364b5aba55d07cc1fe4cb4d1fea7b9d76130b/packages/state-react/src/lib/useReactor.ts#L5) is referenced in several examples but has no documentation:
- it is missing a description
- searching for it in the docs brings up no results

The next best match I can find is https://github.com/tldraw/tldraw/blob/fae364b5aba55d07cc1fe4cb4d1fea7b9d76130b/apps/examples/src/examples/state-store/StateStoreExample.tsx#L77-L80