Bug: broken link in react-reconciler

[xfq]

React version: main branch

Steps To Reproduce

1. Open https://github.com/facebook/react/blob/main/packages/react-reconciler/README.md#practical-examples
2. Click "host config" in "React DOM and its host config"

The current behavior

The page is 404.

The expected behavior

The page should exist.

[kassens]

Fixed by #25788