Repository is a so called monorepo, more information
Package client used is "Yarn" not npm, more information. Using the incorrect package manager will break the monorepo.
Get familiar with Storybook, more information
$ lerna create <your packagename>The new package is created under /packages folder.
Modify the default package.json... see example on core package.
Setup your own storybook environment.... see example on core package.
Test new package by running...
$ yarn storybook