[v2] docs "Apps with Gatsby" overview #6581
Description
This doc exists as a level 2 nav item in next.gatsbyjs.org docs under "Guides" category.
It is meant to be a brief overview of what the section includes as well as any significant notes about what advantages Gatsby provides in that particular aspect of web development.
Some of these overviews already exist; if that's the case, this issue just means it needs to be looked at for editing/revising since the docs haven't been revised in a while.