See the README of the package for more information on the package itself.
You can add the BuildExporter via the Unity Package Manager to your Unity3d project. To do so, to go your Unity3d project's Packages/manifest.json
and add the following line:
{
...
"dependencies": {
...
"io.armet.unity.buildexporter": "https://github.com/ar-met/unity-build-exporter.git?path=/Assets/BuildExporter#1.0.0",
...
}
...
}
Make sure to use the latest release by looking up latest tag.