It's in the docs, so it's not exactly hidden:

> You can edit wikis directly on GitHub, or you can edit wiki files locally.

https://docs.github.com/en/communities/documenting-your-proj...

> Every wiki provides an easy way to clone its contents down to your computer. Once you've created an initial page on GitHub, you can clone the repository to your computer with the provided URL.

Every GitHub wiki you visit also has a section at the bottom that points to that URL with the description

> Clone this wiki locally

as well.