Fix descriptions, update formatting, update header image

[jules-kris]

Closes #issue

• My project tutorial topic has already been approved by the Codédex team.
• My project tutorial file renders properly in mdx.
• My .mdx file follows the project template, as well as what's recommended in the content guidelines.
• The content written is my own, and not plagiarized from other sources.
• All code written is thoroughly functional and commented (or documented).
• I have already completed a self-review of the project tutorial.
• I will comply with changes made or recommended by the Codédex team about my project tutorial.