style: addition of meta in index.html to fix sizing error on mobile

[tomashco]

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

Addition of:
<meta name="viewport" content="width=device-width, initial-scale=1.0">

To prevent viewport to be set at 980px even if it is on mobile, as described here:
Viewport meta tag

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[galvez]

If you can, relay this change to the other examples... 🙏