archive: mention if magic bytes look right, this is esp interesting
archive: mention if magic bytes look right, this is esp interesting

If the data is simply not a nar, it's not surprising there's an error.
However if the data *does* look like a nar, this is arguably worse
and may indicate a corrupt (or partial?) nar instead of simply
pointing nix at nonsense.

dtzWill/nix,dtzWill/nix,dtzWill/nix,dtzWill/nix,dtzWill/nix