In order to avoid confusion, the name Material Nodes Graph is written in the scripts inside Unity. It has been changed to be shared in the Asset Store.
Also, because this repository is created before naming this package, the name of the repository is different from the package names.
In order to install this package, git must be installed on your computer. So you can import packages via git in Unity.
To install this package, go to Package Manager in Unity. Then use Add package from git URL... under + icon. Paste this:
https://github.com/Warwlock/blender-nodes-subgraph.git
If you don't have git installed on your computer then clone this repository to your computer and use Add package from disk....
Then locate your clonned repository folder and find package.json file.
Add-on is located under samples section of package, open Package Manager, under Blender Nodes Graph you will see samples section. Import Blender Add-On from there.
Samples are divided into different render pipelines. Import samples according to your current render pipeline. Samples are located in same place as Blender Add-on.