Setting Up A React Environment: Update import explanations of main.jsx

[Legalunicorn]

Removed mentions of importing React and ReactDOM directly.

Because

Updated the import explanation to match the boilerplate code generated by Vite in the newer version.

This PR

• ReactDOM.createRoot becomes createRoot
• React and ReactDOM removed as imports, changed to StrictMode and createRoot

Issue

Closes #28680

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

[mathdebate09]

Yayy 🚀

[MaoShizhong]

🙏

[Legalunicorn]

Thanks for the opportunity @MaoShizhong :-) Its a very tiny contribution to the lesson but it has been great learning experience for me. Cheers 😃