Ability to require packages in transforms

Hi, i use your tool for creating jscodemod transforms. It really useful, thanks for that.

But I faced situation when i need some package from npm in my transform, for example package for parsing jsdoc, and now i can't do it in the explorer.

So it will be nice to have some opportunity to connect external resources like in jsfiddle.

The issue names no files, tests, or entry points. Begin by locating how JavaScript transforms run in the explorer and determining the intended way to make external npm packages available; done means a transform can use a requested external package in the explorer, with the behavior verified.

Written by the indexing model from the issue text.