add opam metadata for fedora, rhel and oraclelinux distributions
add opam metadata for fedora, rhel and oraclelinux distributions

Signed-off-by: Anil Madhavapeddy <3a02579c191f8558e3fedece867419cb15398b26@recoil.org>

djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs