Fake hashes can be used as placeholders for all the places, where
Nix expression requires a hash, but we don't yet have one.
This should be more convenient than following:
- echo|sha256sum, copy into clipboard, go to editor, paste into previously
edited place
- search nixpkgs for a random package, copy it's hash to cliboard, go to
editor, paste into previously edited place
Nix can add support for these fake hashes. In that case printed error should contain
only 1 hash, so no more problem "which of two hashes from error should I use?"
Idea by irc:Synthetica
68a6b47b8c