(PULL_REQUEST_TEMPLATE) update link to changelog documentation (#34206)

Summary:
I just opened another PR and noticed the changelog page in the wiki redirected to the react native documentation.

## 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
-->

[Internal] [Changed] - Update link to changelog documentation in PULL_REQUEST_TEMPLATE

Pull Request resolved: https://github.com/facebook/react-native/pull/34206

Reviewed By: NickGerleman

Differential Revision: D37920424

Pulled By: cortinico

fbshipit-source-id: f4e47172a13fe5b42c29e320d34816b490a14b6c