docs: update README.md installation section with platform-specific scripts

[q-soriarty]

Problem

README.md still shows the manual installation method (mkdir + cp). The repo now has platform-specific install scripts (install_linux.sh, install_macos.sh, install_windows.ps1) that create symlinks for auto-sync.

Expected behavior

Update the Installation section in README.md to:

• Show the one-liner install script for each platform (Linux, macOS, Windows)
• Explain the symlink advantage (stays in sync with repo)
• Keep the manual method as a fallback
• Document uninstall for each platform

[github-actions]

Closed by #75 (merged into develop).