Setting Up Git: Clarify git email options

[lukegrob]

Because

Due to some confusion around private emails in the github setup, people were were sometimes surprised that gitHub rejected their pushes as they had previously enabled that option in setup.

This PR

• Emphasizes in step 2.1 that they should keep track of their private email (if used) for later
• Rewords the explanation directly around the e-mail config lines to make sure they know that is where they're intended to use it.

Issue

Closes #28739

Additional Information

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