docs: remove legacy useless readme section

[slorber]

fix #9590

we don't need that text anymore and it's probably useless to replace it with something else

[netlify]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 71	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/installation	🟠 69	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/category/getting-started	🟠 77	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog	🟠 75	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 65	🟢 97	🟢 100	🟢 100	🟠 89	Report
/blog/tags/release	🟠 74	🟢 100	🟢 100	🟠 80	🟠 89	Report
/blog/tags	🟠 77	🟢 100	🟢 100	🟢 90	🟠 89	Report