Update `etc` example to not use a real config file

A user noticed the example for `hosts`, took the `mode` permissions literally, and ended up with surprising behavior on their system. Updating the documentation to not reference a real config file which might have real permissions requirements.

Changed files
+1 -1
nixos
modules
system
etc
+1 -1
nixos/modules/system/etc/etc.nix
···
type = types.loaOf types.optionSet;
default = {};
example = literalExample ''
-
{ hosts =
{ source = "/nix/store/.../etc/dir/file.conf.example";
mode = "0440";
};
···
type = types.loaOf types.optionSet;
default = {};
example = literalExample ''
+
{ example-configuration-file =
{ source = "/nix/store/.../etc/dir/file.conf.example";
mode = "0440";
};