[Nix-dev] instructions for setting up apache + mediawiki is broken

[Rob Vermaas]

Hi Bjorn,

> - If no default version, is there at least a way to print a *human
> readable* error message that hints the user about
> services.postgresql.package? The error you get now is pretty horrible.

I have changed the error message, if you have the latest nixpkgs, you
would now see:

  error: user-thrown exception: Option `services.postgresql.package'
not defined and does not have a default value.

Cheers,
Rob