HelloWorld: Set window icon to app-hello-world.png

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/d61ea0da5f7
Pull-request: https://github.com/SerenityOS/serenity/pull/3346

Demos/HelloWorld/main.cpp

@@ -38,6 +38,7 @@ int main(int argc, char** argv)
     auto window = GUI::Window::construct();
     window->resize(240, 160);
     window->set_title("Hello World!");
+    window->set_icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/app-hello-world.png"));
 
     auto& main_widget = window->set_main_widget<GUI::Widget>();
     main_widget.set_fill_with_background_color(true);