pebble: add link to acme nixos test

pkgs/tools/admin/pebble/default.nix

···
 { buildGoPackage
 , fetchFromGitHub
 , lib
+, nixosTests
 }:
 
 let
···
     repo = pname;
     rev = version;
     sha256 = "1piwzzfqsdx6s2niczzp4mf4r3qn9nfdgpn7882g52cmmm0vzks2";
+  };
+
+  passthru.tests = {
+    smoke-test = nixosTests.acme;
   };
 
   meta = {