docs: enhance docs about Markdown TOC and metadata

[Josh-Cena]

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

Another batch-update to update the docs with all confusions I've explained recently.

Test Plan

Test links

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

[netlify]

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	66
🟢 Accessibility	100
🟢 Best practices	92
🟢 SEO	100
🟢 PWA	90

Lighthouse ran on https://deploy-preview-7278--docusaurus-2.netlify.app/

[github-actions]

Size Change: -684 B (0%)

Total Size: 805 kB

Filename	Size	Change
website/.docusaurus/globalData.json	50.5 kB	-195 B (0%)
website/build/assets/js/main.********.js	609 kB	-489 B (0%)

ℹ️ View Unchanged

Filename	Size
website/build/assets/css/styles.********.css	107 kB
website/build/index.html	38.8 kB

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