docs(website): fix broken external links wrongly modified to use the .mdx extension (ex: github README.mdx)

[Kesyau]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

The links to browserslist's doc are broken.

Test Plan

Preview.

Test links

Deploy preview: https://deploy-preview-8509--docusaurus-2.netlify.app/docs/browser-support#read-more

Related issues/PRs

None.

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	0df3774
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/63b6be124079360008407bec
😎 Deploy Preview	https://deploy-preview-8509--docusaurus-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

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

[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 80	🟢 97	🟢 100	🟢 100	🟢 90	Report
/docs/installation	🟠 78	🟢 100	🟢 100	🟢 100	🟢 90	Report

[slorber]

Thanks, I recently converted all docs to .mdx and was a bit too aggressive when converting markdown links 😅

Will fix the few bad links in this PR