Git Basics lesson: Add link to Git Exercises in Additional Resources

[JulianColoma]

Because

To provide users with a practical way to reinforce what they've learned in the course through interactive exercises.

This PR

Adds a link to the Git exercises on W3Schools in the additional resources section.

Issue

Additional Information

Link added: Git Exercises - W3Schools.
The exercises on this page allow users to practice Git commands and concepts in an interactive environment.

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