Update announcement bar (put the link in new line - mobile screens)

[hslee2008]

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.

Motivation

Very hard to understand at first sight what the sign is about in mobile.
Also, it is very hard to click the link in the bar.

Test Plan

Test links

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

[netlify]

✅ [V2]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 56	🟢 100	🟢 100	🟢 100	🟢 90	Report
/docs/installation	🟠 84	🟢 94	🟢 100	🟢 100	🟢 90	Report