• Disabling wikis - User Documentation
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Source

You can turn wikis off for your repository if you decide not to use them.

1. On GitHub, navigate to the main page of the repository.

2. Under your repository name, click Settings.

3. Under Features, unselect Wiki.

When you turn off a wiki, the content is hidden, but not erased. If you choose to re-enable wikis later, your previous pages will be restored.