Adding a copy utility (thx Mats)

pkgs/default.nix

@@ -36,5 +36,17 @@ self: super:
             --replace 'system.nixosVersion' 'system.nixos.version'
     '';
   });
+  # Originally from Mats Rauhala ®2018
+  copy = super.writeScriptBin "copy" ''
+    function clean() {
+      sleep 10
+      echo cleaning
+      ${super.xclip}/bin/xclip -sel clipboard -i /dev/null
+    }
+
+    ${super.xclip}/bin/xclip -sel clipboard < /dev/stdin
+
+    clean &
+  '';
 }