as proposed by mclovin on IRC:
> 14:21 < mclovin> I was thinking, could we archive one more opam instance ?
> 14:21 < mclovin> I was thinking of: https://coq.inria.fr/opam/released/
> 14:21 < mclovin> the official opam instance is mainly for ocaml packages, but this one contains a lot of Coq related packages