Added reference to use the codesandbox template

[sammychinedu2ky]

Motivation

Made this pull request to make known CodeSandbox support for Docusaurus

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

I only added a tip admonition referencing Codesandbox support for Docusaurus. The admonition was added to the introduction docs and also the installation docs

Related PRs

It is related to this PR #3717

[netlify]

❌ [V1] Deploy preview failure
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[github-actions]

Size Change: +1 B (0%)

Total Size: 26.8 kB

ℹ️ View Unchanged

Filename	Size	Change
website/build/blog/2017/12/14/introducing-docusaurus/index.html	20.8 kB	0 B
website/build/docs/introduction/index.html	180 B	0 B
website/build/index.html	5.86 kB	+1 B (0%)

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[netlify]

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	78
🟢 Accessibility	99
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-4061--docusaurus-2.netlify.app/classic/