Hi Felix,
By installing the demo, the Wiki page should have been imported.
My best guess is that something went wrong during the import. In that case, it’s recommended to address the issue right now as it might lead to other problems in the future. We really suggest you to reset your WordPress database using WP Reset (https://wordpress.org/plugins/wp-reset/) and start fresh with our setup wizard.
You can easily install the theme by relaunching the setup wizard, as it will programmatically do every steps for you.
We’re waiting for your feedback.
Regards,