[Docs] Next.js - introduction - content authoring concepts

[anastasiya29]

Next.js docs - "Content Authoring Concepts"

This page was created as a pre-req for the "Layout, Components, and Component Factory Concepts" page.
After release, we will need to change any links to the sample app from using the dev branch to using master.

For testing, use http://localhost:3001/docs/nextjs/introduction/content-authoring-concepts

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update (non-breaking change; modified files are limited to the /docs directory)

[nickwesselman]

Great addition, glad we could pull in this content