docs: clarify behaviour of <Tabs> children

[homotechsual]

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

Test Plan

Test links

Deploy preview: https://deploy-preview-_____--docusaurus-2.netlify.app/

Related issues/PRs

[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 75	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/installation	🟠 74	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/category/getting-started	🟠 64	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog	🟠 61	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 52	🟢 97	🟢 100	🟢 100	🟠 89	Report
/blog/tags/release	🟠 61	🟢 100	🟢 100	🟠 80	🟠 89	Report
/blog/tags	🟠 86	🟢 100	🟢 100	🟢 90	🟠 89	Report

[Josh-Cena]

Bad branch? You seem to have removed a lot of stuff...

[homotechsual]

Bad branch? You seem to have removed a lot of stuff...

Yeah I pushed from a very out of date local copy. Closing - will recreate.