add getting started video 07: installing global packages

Here's the seventh Getting Started video. If you'd like to review and comment, please feel free to!

https://www.youtube.com/watch?v=Opg5GS7s98E

Before merge, these must be done:
- [x] @rod11 reviews
- [x] @iarna reviews
- [x] Lin smooths out vocals
- [x] Lin adds text