add getting started video 04: installing local npm packages

Here's the fourth Getting Started video. If you'd like to review and comment, please feel free to!

https://www.youtube.com/watch?v=yzdK75mckDI

Before merge, these must be done:
- [x] @rod11 reviews
- [x] @seldo reviews
- [x] Lin smooths out vocals
- [x] Lin adds text