The README had incorrect build instructions:
- apk.nix was shown with --arg mainModule, but it doesn't accept that parameter
- Consumer project section showed importing apk.nix directly with mainModule/consumerCabalFile,
  but the real pattern is creating your own nix files that import lib.nix
- iOS setup showed manual cp + xcodegen, but the real flow uses mkSimulatorApp

Rewrote the consumer sections to match prrrrrrrrr's working build scripts:
- Android: show nix/android.nix with mkAndroidLib + cross-deps.nix, nix/apk.nix with mkApk
- Include install.sh and install-wear.sh script examples
- iOS: show nix/ios.nix with mkIOSLib + ios-deps.nix, nix/ios-app.nix with mkSimulatorApp
- Include setup-ios.sh script pattern with xcodegen

Prompt: fix the build instructions for hatter in the readme, look at prrrrrrrrrr how it's build via those scripts, those are correct, use that as a reference to repair the build instructions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>