note about optional subcommands
//! + `make-cookie pound 50`
//! + `make-cookie sparkle -mmm --color "green"`
//! + `make-cookie finish 130 glaze 3`
+//!
+//! ### Optional subcommands
+//!
+//! A nested subcommand can be marked optional:
+//!
+//! #[derive(StructOpt)]
+//! #[structopt(name = "foo")]
+//! struct Foo {
+//! file: String,
+//! #[structopt(subcommand)]
+//! cmd: Option<Command>
+//! }
+//!
+//! #[derive(StructOpt)]
+//! enum Command {
+//! Bar {},
+//! Baz {},
+//! Quux {}
+//! }
extern crate proc_macro;
extern crate syn;
