Fix URL in README

[MasayaTahara]

Summary

When clicking on the link to the React website, a "Page Not Found" error occurred. The URL of the link has been corrected to the top page.

How did you test this change?

I clicked on the modified link and confirmed that no error occurred.

[sizebot]

Comparing: cb6c619...3f62c0b

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	127.39 kB	127.39 kB	=	40.59 kB	40.59 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	130.21 kB	130.21 kB	=	41.51 kB	41.51 kB
facebook-www/ReactDOM-prod.classic.js	=	405.44 kB	405.44 kB	=	75.05 kB	75.05 kB
facebook-www/ReactDOM-prod.modern.js	=	394.03 kB	394.03 kB	=	73.34 kB	73.34 kB
facebook-www/ReactDOMForked-prod.classic.js	=	405.44 kB	405.44 kB	=	75.05 kB	75.05 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 3f62c0b

[stale]

This pull request has been automatically marked as stale. If this pull request is still relevant, please leave any comment (for example, "bump"), and we'll keep it open. We are sorry that we haven't been able to prioritize reviewing it yet. Your contribution is very much appreciated.

[kassens]

Thanks, this has been fixed.