Add Freqens

[clement-spiers]

Pull Request Template

Please ensure all items below are checked before creating a pull request:

• [x] My changes were made in the resources folder, not in the auto-generated README.md file or db folder
• [x] The resource is highly or exclusively related to programming and development
• [x] My submission is formatted according to the guidelines in the contributing guide
• [x] My submission is ordered alphabetically based on the resource name
• [x] My submission has a useful description
• [x] I have searched the repository for any relevant issues or pull requests

[github-actions[bot]]

New resource link: https://www.freqens.com/

[marcelscruz]

Thank you for the contribution, but it's not a resource highly or exclusively related to programming and development, as mentioned in the CONTRIBUTING guide.