chore(derive): Ensure license is recorded for subcommand

clap_derive/src/derives/subcommand.rs

@@ -1,3 +1,16 @@
+// Copyright 2018 Guillaume Pinot (@TeXitoi) <[email protected]>,
+// Kevin Knapp (@kbknapp) <[email protected]>, and
+// Andrew Hobden (@hoverbear) <[email protected]>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// This work was derived from Structopt (https://github.com/TeXitoi/structopt)
+// commit#ea76fa1b1b273e65e3b0b1046643715b49bec51f which is licensed under the
+// MIT/Apache 2.0 license.
 use crate::{
     attrs::{Attrs, Kind, Name, DEFAULT_CASING, DEFAULT_ENV_CASING},
     derives::args,