docs: typo fix Lighting → Lightning

[vsn4ik]

Summary

• Fix typo in the README, Lighting CSS → Lightning CSS

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[netlify]

✅ Deploy Preview for rsbuild ready!

Name	Link
🔨 Latest commit	aea3161
🔍 Latest deploy log	https://app.netlify.com/sites/rsbuild/deploys/66b377ac7aca4a0008febdb4
😎 Deploy Preview	https://deploy-preview-3154--rsbuild.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 74 (🔴 down 17 from production) Accessibility: 97 (no change from production) Best Practices: 100 (no change from production) SEO: 92 (no change from production) PWA: - View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[chenjiahan]

Thanks!