To get the UE4 editor for Linux, you need to build it yourself from the source (Github). You’re on the right track in that regard.
- Follow these instructions (the quickstart you linked has them as well) to connect your Github to Epic account.
- You should then be able to visit the repo on GitHub without 404ing, the authorization might take a bit of time
- Git clone the source code from the release branch or download as ZIP via the green button
- Follow the instructions for Step 3. on from the guide to build the Editor for Linux