[kolebayev]

Summary

Rewrites the README so it reads for someone deciding whether to download the
app, not for someone about to work on it. Adds a screenshot of the app.

Changes

• New tagline: "iPod without iTunes — a native macOS app that manages your library"
• Screenshot at assets/screenshot.png, shown under the header
• Dropped the intro Note and the whole Safety section
• Features rewritten in plain language; the device/SysInfo detail is gone
• Installation now spells out the xattr -dr com.apple.quarantine step
  instead of burying it in a Tip
• Requirements trimmed to macOS, Apple Silicon, and an iPod Classic

Test plan

Rendered the README locally; every anchor in the header nav still resolves and
the screenshot path is tracked (docs/ is gitignored, hence assets/).