Generate nix expressions from npmjs.org!
npm2nix node-packages.json node-packages.generated.nix
npm2nix expects the passed JSON file to be a list of strings and at most one
object. Strings are taken as the name of the package. The object must be
a valid dependencies object for an for an npm packages.json file.
Alternatively, the passed JSON file can be an npm package.json, in which
case the expressions for its dependencies will be generated.