Comment (by Roland Haas):

There is no DOI to cite yet, all citations are still the ones listed on http://einsteintoolkit.org/citation.html . The change in policy is still up for discussion and will be brought up in today’s ET call.

--
Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2259/cannot-find-doi-for-einstein-toolkit