I've built a little web-based tool called [ForceNPM][1] that makes it super easy to add NPM packages to Salesforce. Check it out:
  
[<img src="/uploads/2016/08/02092614/forcenpm.gif" alt="forcenpm" width="854" height="480" class="alignnone size-full wp-image-4236" style="border: solid 1px" />][1]

[Give ForceNPM a try!][1]

The code is [on GitHub][2] so if you'd like to deploy this on your own Heroku app or other infrastructure, you can do that. Let me know how it goes!

 [1]: https://forcenpm.herokuapp.com
 [2]: https://github.com/jamesward/forcenpm