add getting started video 04: installing local npm packages

Here's the first Getting Started video. If you'd like to review and comment, please feel free to!

https://www.youtube.com/watch?v=MIoD6tH9dhQ

Before merge, these must be done:
- [ ] @rod11 reviews
- [ ] @iarna reviews
- [ ] Lin smooths out vocals
- [ ] Lin adds text