g := &FSGenerator{
	FS: NewWritableDirFS("out"),
}

err := g.Generate(
    context.Background(),
	PlainFile("README.md", "# drydock"),
	Dir("bin",
		Dir("cli",
			PlainFile("main.go", "package main"),
		),
	),
	Dir("pkg",
		PlainFile("README.md", "how to use this thing"),
		Dir("cli",
			PlainFile("cli.go", "package cli..."),
			PlainFile("run.go", "package cli...run..."),
		),
	),
)