You can click on the code button in the top right, copy that or just copy this
[email protected]:dropecho/unity_custom_scene_modes.git
Open unity, and open the package manager, in the dropdown select install from git, and paste that in.
It should then show up in the list of installed packages
Use the context menu to create a "Dropecho/Custom Scene Draw Mode" Asset. Assign a shader to the new asset and it should be available in the scene view modes dropdown.
A simple example showing the normal directions as a colored texture is included.