The ECmean package has been removed from the EC-Earth 3 repository, because it
is maintained now as part of the ece3-postproc project on GitHub at
https://github.com/plesager/ece3-postproc.git. See issue #550 at the EC-Earth
Development Portal for details and discussion.

I order to clone (check out) ece3-postproc, use the command:

> git clone https://github.com/plesager/ece3-postproc.git