Initial outline for npm-run-script chapter

Very rudimentary outline for the `npm-run-script` chapter as discussed in #22. The purpose of this outline is to:

1. Get feedback on the naming of the sections (pages?) and headings.
2. Have a shell that we are happy with so we can start adding content.

I've tried to organize things such that there is a natural flow or progression from the introduction to the actual task writing examples that does not assume too much about what the reader already knows.