I can't install cardboard-xr-plugin, what should I do?

Question

Unity

tried installing the package via git

https://github.com/googlevr/cardboard-xr-plugin.git

(taken from google site)

error, found another one on github

https://github.com/googlevr/cardboard-xr-plugin.git

doesn't work either, error:

Error adding package: https://github.com/googlevr/cardboard-xr-plugin.git.
UnityEditor.EditorApplication:Internal_CallUpdateFunctions ()

where can i get it? worker important, don't understand