Better post-install markdown file generation.

Hey,

Great lib! I've found it really useful.

The only thing I don't think works is the resulting README file.

It's quite bulky and doesn't help when you are trying to get your head around what's been generated and trying to customize and add your own code.

I would suggest modifying it so that:

It generates a new project-specific `README.md` file intended for the final consumer, with:
- Project name
- section: "Introduction"
- section: "Importing library"
- section: "NPM Scripts"

It contains a new `tools/README.md` file, intended for the package developer, with:
- section "Features" - information about how the package works
- section "Build" - information about Rollup, etc
- section "Deployment" - information about releases, hooks, tools, etc
- section "Customisation" - essentially the FAQs refactored to be a how-to on the change you want, what to update or remove, and why
- section "Resources" useful resources

The project's main readme should just have info about the project, should only exist on GitHub for **this** project, and should be deleted after the `install` script:

- image: Terminal
- section "Features"
- section "Development" link to `DEVELOPMENT.md` readme above
- section "Projects"
- section "Credits"

I may PR this.