chore: update all website links about react (#36638)

Summary:
New website of React is online, so some links about react should be also updated in README.md.

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[General] [Fixed] - Fix some links about react in readme

Pull Request resolved: https://github.com/facebook/react-native/pull/36638

Test Plan: The PR just changes some links in readme, don't need to test.

Reviewed By: jacdebug

Differential Revision: D44959199

Pulled By: blakef

fbshipit-source-id: 14a66a2d2b086fbe16f715c621c59a6d8d6ee698