Add a separate file to the volta pin directive

[huafengThunder]

No description provided.

[chriskrycho]

If you're meaning adding the ability to have volta pin put its output in a separate file, rather than as part of package.json, that's a good idea and something we have wanted for quite a while; see #282, #983, and #959 for details. I'm going to close this on the assumption it is covered by one of those, but please feel free to reopen and add some clarifying text to your original write-up if not!