📝 Conversion Guides - Make Gatsby & WordPress conversion guides stylistically consistent

[Calinator444]

CC: @Marxoz, @isaaclombardssw

💫 Describe the Issue With the Current Docs

The documentation for converting Gatsby blogs to Tina is inconsistent with the documentation for converting WordPress blogs to Tina.

📝 Outline the Proposed Change

Ideally, the Gatsby Blog should follow the format below, which includes having relevant headings or each section

• Introduction
• Prerequesites
• Getting Started
• Arbitrary number of steps (with level 3 headings where applicable)

💼 Tasks

• Restructure the Gatsby guide to fit the format outlined above
• Get you changes checked by a TinaCMS maintainer

➕ More Information

Here's the links to each guide:

• Converting WordPress to Tina: https://tina.io/docs/guides/converting-wordpress-to-tina
• Converting Gatsby to Tina: https://tina.io/docs/guides/converting-gatsby-to-tina
• I've uploaded a branch that includes the repo fully migrated to TinaCMS for reference: https://github.com/tinacms/gatsby-mdx-example-blog/tree/tutorial-endpoint