Gatsby: Content migration - create Layout Components doc

[shannonbux]

Issue Context

This issue is part of the content migration project (#8103), which is meant to take existing content and repurpose it so it's easier to find in the docs.

Motivation

We are doing this because many people have written excellent content that we want to canonize and maintain so more people can find it and benefit from it.

Steps to resolve this issue

Review the Gatsby docs approach

• [ ] Read the Style Guide and follow it in order for your PR to be accepted. Pay special attention to the templates.
  
  
  
  • Style Guide: https://www.gatsbyjs.org/docs/gatsby-style-guide/
  
  
  • Docs Templates: https://www.gatsbyjs.org/docs/templates/
  
  
  • Example of a similar article: [todo: find and link to appropriate article for new issue]
  
  

Draft the doc

• [ ] Create a new file named layout-components.md in the docs source directory.
• [ ] Begin the newly-created markdown file with the following frontmatter:

title: Layout components
---

• [ ] Use the following reference material as a primary starting point to draft the new doc:
  https://www.gatsbyjs.org/tutorial/part-three/

  Make sure you rewrite and adjust the content to follow the format listed in these resources:

  • Docs Templates: https://www.gatsbyjs.org/docs/templates/
  • Example of a guide to imitate: https://www.gatsbyjs.org/docs/deploying-to-s3-cloudfront
• [ ] Review the following additional reference materials, and integrate any additional detail, if helpful:
• https://www.gatsbyjs.org/blog/2018-06-08-life-after-layouts/
• [ ] Add a link to the doc-links.ymlfile so your newly created doc shows up in the sidebar navigation of the .org site!

Open a pull request

• [ ] Open a pull request with your work. In the description, include the words "closes #8845"

[eunicode]

Hi, can I take a stab (Halloween pun intended) at this?

[shannonbux]

Yes, just label it with Hacktoberfest - claimed and then mention this issue in your PR! Thanks @eunicode!