pebble: add link to acme nixos test

pkgs/tools/admin/pebble/default.nix

@@ -1,6 +1,7 @@
 { buildGoPackage
 , fetchFromGitHub
 , lib
+, nixosTests
 }:
 
 let
@@ -17,6 +18,10 @@ in buildGoPackage {
     sha256 = "1piwzzfqsdx6s2niczzp4mf4r3qn9nfdgpn7882g52cmmm0vzks2";
   };
 
+  passthru.tests = {
+    smoke-test = nixosTests.acme;
+  };
+
   meta = {
     homepage = "https://github.com/letsencrypt/pebble";
     description = "A miniature version of Boulder, Pebble is a small RFC 8555 ACME test server not suited for a production CA";