Improve Android build and run instructions for new contributors

[2024si96553-droid]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

The README previously lacked clear, step-by-step instructions for building and running the project in Android Studio.
This can confuse new contributors who are unfamiliar with the required Android SDK level, build variants, or emulator setup.

This PR adds:

• A dedicated "Build & Run" section
• Recommended Android Studio version
• Required SDK version and Gradle sync notes
• Steps for selecting the correct build variant
• Emulator requirements for testing

These improvements help new contributors set up the development environment quickly and avoid common setup errors.

Tests performed

Documentation-only change.
No code, UI, or functional behavior affected by this update.

Before & after preview

Not applicable (documentation change only).

Closes the following issue(s)

No related issue.

Checklist

• I read the contribution guidelines.
• I manually reviewed my changes (formatting, clarity, no typos).
• I updated the "Unreleased" section in CHANGELOG.md (not applicable for docs-only change).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• All checks are passing.