flutterアプリデザイン手順メモ アプリアイコンの追加 https://qiita.com/k-nasa/items/33426af4d396b581c101 スプラッシュ画面作成 https://yaba-blog.com/flutter-splash-screen/ floatingActionButtonボタンに文字を入れる https://api.flutter.dev/flutter/material/FloatingActionButton-class.html
