Update README.md (#32277)
Update README.md (#32277)

Summary:
Update the showcase url to the right url.

When I did check out the repository and I was about to navigate to showcase. I found out the url was wrong.

## Changelog

<!-- Help reviewers and the release process by writing your own changelog entry. For an example, see:
https://github.com/facebook/react-native/wiki/Changelog
-->

[General] [Changed] - Changed the showcase URL

Pull Request resolved: https://github.com/facebook/react-native/pull/32277

Reviewed By: lunaleaps

Differential Revision: D31206326

Pulled By: cortinico

fbshipit-source-id: a4092e9bb74d9a9cc68d7252aa131083dd38b6ca

janicduplessis/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,facebook/react-native,javache/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,facebook/react-native,facebook/react-native,javache/react-native,javache/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,javache/react-native,facebook/react-native