Fix Example app web README

[Kicu]

Details

• updates README for Example App, to mention usage of npm on top level; if one uses yarn there are webpack errors there
• regenerated yarn.lock inside /Example

What this fixes

It makes it more clear how to run web Example

Checklist

• I have described the bug/issue
• I have provided reproduction in Example App
• I have tested that solution works on Example App on all platforms:
  • Android
  • iOS
  • Web

Screenshots/Videos

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[Kicu]

@mountiny 🙏 this breaks nothing, just docs and lockfiles

[gedu]

LGTM, that is the flow I have to take to run the Example app

[Kicu]

I have read the CLA Document and I hereby sign the CLA

[mountiny]

Thanks!