Improve README: features, screenshots, platform setup, downloads, contribution & usage docs

[mariobehling]

The readme was good when the project started, but now it is missing important information. It provides basic Flutter boilerplate and minimal run instructions, but it doesn’t yet explain the Magic ePaper App to new users and contributors.

As the Readme is also not super long I do not think we need a table of contents. Please remove that.

Update the Readme with the following info:

• Add a concise tagline + expanded description of the app and its goals.

• Include screenshots or a short GIF (Create & Transfer, NFC read/write, result).

• Add Features section (bullets).

• Add Downloads section (TestFlight, Google Play Beta, and/or GitHub Releases) — or note status if pending.

• Document Requirements (Flutter/Dart versions, Android Studio/Xcode versions).

• Document Platform setup & permissions:

  • Android: NFC/Bluetooth/file permissions, Gradle config notes.
  • iOS: capabilities/entitlements (NFC, etc.), minimum iOS version.

• Add Usage: step-by-step to create an image and write to a badge; link to sample assets.

• Add Compatibility matrix: supported e-paper sizes/badge models; supported platforms (Android/iOS/Web/Desktop) and minimum OS versions.

• Add Troubleshooting/FAQ (connection issues, write failures, unsupported tag, build errors).

• Add Contributing: link to CONTRIBUTING.md and CODE_OF_CONDUCT.md (create if missing); how to run tests and lint.

• Add Architecture & folder structure overview (where NFC, localization, assets live).

• Add Localization notes (ARB files location, how to add/update languages).

• Add Badges: License, CI status, maybe platform badges.

• Add Maintainers & community links (issues, discussions, FOSSASIA contact).

• Add Security/Privacy note (what data is used/stored; no analytics if true).

• Add Changelog/Roadmap links if available.

Acceptance Criteria

• A new contributor can clone, configure platform permissions, build, and perform a basic NFC write following the README alone.
• Users can see what devices and display sizes are supported and where to get the app.
• Contributors know how to run tests/lint and where to add localization and features.
• README includes screenshots/GIFs and clear links to contributing and community docs.