function linkCmd (cwd, argv) {
	const names = argv._.slice(1)

	if (names.length) {
		const localNodeModules = path.join(cwd, 'node_modules')
		const init = mkdirp(localNodeModules)
		return concatStatic(init, ArrayObservable.create(names)
			::mergeMap((name) => linkFromGlobal(cwd, name)))
	}

	const init = concatStatic(
		mkdirp(config.globalNodeModules),
		mkdirp(config.globalBin))
	return concatStatic(init, linkToGlobal(cwd))
}
can be used in two ways:
1. in order to globally _expose_ the current package (`ied link`).
2. in order to use a previously globally _exposed_ package (`ied link tap`).

useful for local development when you want to use a dependency in a
different project without publishing to the npm registry / installing from
local FS.

create a symlink either in the global `node_modules` directory (`ied link`)
or in the project's `node_modules` directory (e.g. `ied link tap` would
create a symlink in `current-project/node_modules/tap` pointing to a
globally installed tap version).

@param  {String} cwd - current working directory.
@param  {Object} argv - parsed command line arguments.
@return {Observable} - observable sequence.