Update storybook documentation to include design system

[daniele-zurico]

the Storybook introduction page explains how you can install and use the components in your project however the styling part is quite incomplete because it doesn't explain the different ways how you can use the component and what to expect.

I suggest to include some documentation in the different ways you can use our component:

• the look and feel of a button as soon as you install the library
• the look and feel of a button with className (so you define the entire CSS) + video that show it
• the look and feel of a button with the design system (provide all the examples needed to use it in your project) + video that show it

We should ask ourselves a question... reading the introduction page are we able to understand all the capabilities of the library and how to use it?

[daniele-zurico]

closed by #625