[docs] Update the installation guides to use the next tag

[mnajdova]

I noticed that we were missing the <!-- #default-branch-switch --> statement on the installation guides. I've udpated the readmes and the docs and added the comment.

[mui-bot]

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• docs/data/base/getting-started/quickstart/quickstart.md
• docs/data/base/guides/working-with-tailwind-css/working-with-tailwind-css.md
• docs/data/joy/getting-started/installation/installation.md
• docs/data/joy/integrations/icon-libraries/icon-libraries.md
• docs/data/material/components/about-the-lab/about-the-lab.md

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[danilo-leal]

Should we add this callout to each installation page? The X components have it:

[mnajdova]

Should we add this callout to each installation page? The X components have it:

Sure we can add it 👍 Let me update the PR.

[DiegoAndai]

Do you think we should do this right away? I think we should add a callout to opt-in to the next version instead of updating the command right away, at least until the beta release.

[danilo-leal]

I guess it's fine because the callout would only be visible if you're viewing the docs with the v6 version selected, right? If you're within the v5 version of the docs, I'd agree, yeah, that you shouldn't see the installation commands defaulting to v6.

[mnajdova]

Yes, the callout and the instructions are shown in next.mui.com if someone comes to this subdomain they should see next as a tag, and the callout makes sense just as a precaution

[DiegoAndai]

Oh! My bad, that makes sense