React Router: Replace article linked to under additional resources

[Maddily]

Because

The medium article on loaders linked to under additional resources has become a member-only story. This is a replacement for that article.

This PR

• Replaces the medium article link with another for an article on loaders on DEV Community.

Issue

Closes #29376

Additional Information

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