Added a link to an imagekit.io article in the "Additional Resources" section of the "Links and Images" lesson. The article compares JPEG, PNG, GIF, and WebP formats, helping learners choose the right format for web use.

Because

It is a great resource for those who want to understand more deeply:

• the difference between the different types of image formats
• and which image format to use for different cases.

This PR

• add a link to Additional resources section

Issue

Closes #XXXXX

Additional Information

Pull Request Requirements

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