# Pastebin oEywH2fq
~ $ < ~/.nixpkgs/config.nix
{
  allowUnfree = true;
  overlays = [ import /home/repos/config/pkgs ];
}
~ $ head -n3 /home/repos/config/pkgs/default.nix
self: super:
{
  overlaydemo = self.buildEnv { name = "overlaydemo"; paths = [ ctags ]; };
~ $ nix-env -i overlaydemo
error: selector ‘overlaydemo’ matches no derivations
zsh: exit 1     nix-env -i overlaydemo