Document CommandOptions.env

Functions which behave differently based on environment variables should
pass the environment to allow caller control (without changing the
global state) and to facilitate testing.  Document this.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

Author: kevinoid

bin/cmd.js

@@ -15,10 +15,12 @@ const modulename = require('..');
 /** Options for command entry points.
  *
  * @typedef {{
+ *   env: !object<string,string>,
  *   stdin: !module:stream.Readable,
  *   stdout: !module:stream.Writable,
  *   stderr: !module:stream.Writable
  * }} CommandOptions
+ * @property {!object<string,string>} env Environment variables.
  * @property {!module:stream.Readable} stdin Stream from which input is read.
  * @property {!module:stream.Writable} stdout Stream to which output is
  * written.