Fix documentation links

Summary:
Old link gives `404 File not found`.

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Closes #17501

Differential Revision: D6688183

Pulled By: hramos

fbshipit-source-id: d17cea84d3cbab551041c9bb15e328aa5826b6ea

Author: Taym95

react-native-git-upgrade/README.md

@@ -6,7 +6,7 @@ It uses Git under the hood to automatically resolve merge conflicts in project t
 
 ## Usage
 
-See the [Upgrading docs](https://facebook.github.io/react-native/releases/next/docs/upgrading.html) on the React Native website.
+See the [Upgrading docs](https://facebook.github.io/react-native/docs/upgrading.html) on the React Native website.
 
 Basic usage: