Change documentation structure to include how-tos and more tutorials

Documentation system: https://documentation.divio.com/

Example:

Source: https://www.gatsbyjs.com/docs/

Start by reading the linked Divio documentation system and comparing its how-to and tutorial structure with the Gatsby documentation example. Then inspect the repository's current documentation organization; done means the structure clearly includes how-tos and tutorials in a consistent arrangement.

Written by the indexing model from the issue text.