Fix hyperlink issue #231

[gulcing]

Pull Request checklist

Before you start

• Read CONTRIBUTING.md.
• Create an issue to discuss your idea. This allows your contributions to be incorporated into the tutorial.

Tasks

• Give this pull request a descriptive title.
• If you are contributing to existing lesson materials, please make sure the content conforms to the Lesson development section in CONTRIBUTING.md and does not contain any spelling or grammatical errors.
• If you are making a new episode, please make sure the content conforms to the Lesson organization and Lesson formatting sections in CONTRIBUTING.md and does not contain any spelling or grammatical errors.
• Preferably Codacy checks pass. Status can be seen below your pull request. If there is an error, click the link to find out why.
• Preview changes on your machine before pushing them to GitHub by running make serve, alternatively make docker-serve. Please see the Previewing your changes locally section in CONTRIBUTING.md for installation instructions.
• All code instructions have been tested.

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Closes {issue #231}

[LisaBock]

Thank you so much @gulcing ! Looks great to me!