Update README.md

[eve-at]

Description

Add https://playground.com/ to Image Generation section

Checklist

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• [x] Read and understood the Contributing Guidelines.
• [x] Checked that your changes align with the repository's goals and content.
• [x] The submission is not already present in the list

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[eve-at]

@Hyraze Thank you for creating such a library. Very good idea!