cliphist: add contribution scripts

cliphist has some scrips that do some of the work of integrating it with
fzf, rofi & wofi. They weren't present in the derivation yet, so this
commit is adding them.

scripts: https://github.com/sentriz/cliphist/tree/master/contrib

pkgs/tools/wayland/cliphist/default.nix

@@ -1,4 +1,8 @@
-{ lib, buildGoModule, fetchFromGitHub }:
+{
+  lib,
+  buildGoModule,
+  fetchFromGitHub,
+}:
 
 buildGoModule rec {
   pname = "cliphist";
@@ -13,6 +17,10 @@ buildGoModule rec {
 
   vendorHash = "sha256-O4jOFWygmFxm8ydOq1xtB1DESyWpFGXeSp8a6tT+too=";
 
+  postInstall = ''
+    cp ${src}/contrib/* $out/bin/
+  '';
+
   meta = with lib; {
     description = "Wayland clipboard manager";
     homepage = "https://github.com/sentriz/cliphist";