A Deeper Look at Git: Move default branch name note box to top of assignment

[mao-sz]

Because

Makes more sense leading the assignments rather than trailing them.

This PR

• Moves note box placement
• Fixes note box heading case for style guide (sentence case)

Issue

N/A

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide