docs: clarify MDX version used

[lex111]

Motivation

See #4029 (comment)

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Preview

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

[netlify]

✔️ [V2]

🔨 Explore the source changes: 58c78ac

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/61435cef385cb20007a9137f

😎 Browse the preview: https://deploy-preview-5575--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	76
🟢 Accessibility	98
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-5575--docusaurus-2.netlify.app/

[github-actions]

Size Change: -4 B (0%)

Total Size: 826 kB

ℹ️ View Unchanged

Filename	Size	Change
website/.docusaurus/globalData.json	36.7 kB	0 B
website/build/assets/css/styles.********.css	94 kB	0 B
website/build/assets/js/main.********.js	414 kB	0 B
website/build/blog/2017/12/14/introducing-docusaurus/index.html	67 kB	0 B
website/build/blog/index.html	38.1 kB	0 B
website/build/docs/index.html	44.5 kB	-2 B (0%)
website/build/docs/installation/index.html	52.8 kB	-2 B (0%)
website/build/index.html	30.8 kB	0 B
website/build/tests/docs/index.html	25.4 kB	0 B
website/build/tests/docs/standalone/index.html	23 kB	0 B

_{compressed-size-action}

[Josh-Cena]

The link still directs to v2. Shouldn't the v1 link be used?

[lex111]

Does MDX have site designed for the current v1? https://v1.mdxjs.com/ is very outdated site.

[Josh-Cena]

Hmm, this link you posted in the other issue seems good for now? https://mdx-git-renovate-babel-monorepo-mdx.vercel.app/

[lex111]

This is actually preview deploy from one of PR from mdxjs repo. I'm not sure if it should be used for this link, but it might be worth using for MDX playground link on 26 line.

[Josh-Cena]

I see, interesting that the deploy preview link is so human readable🧐