fix(create-docusaurus): tutorial and init template improvements

[slorber]

Motivation

The tutorial explicit sidebar must contain the tutorial-basics/create-a-document doc, so that the sidebar remains visible while browsing the doc suggesting to create that manual sidebar in the first place. See also feedback #4610 (comment)

Also mention site config + themeConfig in the extras

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	b65fbf1
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/63108e1923fe680008ef9995
😎 Deploy Preview	https://deploy-preview-8032--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
/	🟠 77	🟢 98	🟢 100	🟢 100	🟠 80	Report
/docs/installation	🟠 76	🟢 100	🟢 100	🟢 100	🟢 90	Report

[github-actions]

Size Change: 0 B

Total Size: 814 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	52.5 kB
website/build/assets/css/styles.********.css	111 kB
website/build/assets/js/main.********.js	610 kB
website/build/index.html	40.9 kB

_{compressed-size-action}