Link checker for tutorial

[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 #181

[gulcing]

Hi @LisaBock, could you please look at what I've done? I am getting error regarding the config file.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}