Mention parseObject in orphan perf TODO

c++/src/capnp/compat/json.c++

@@ -417,7 +417,7 @@ public:
   void parseArray(JsonValue::Builder& output) {
     // TODO(perf): Using orphans leaves holes in the message. It's expected
     // that a JsonValue is used for interop, and won't be sent or written as a
-    // Cap'n Proto message.
+    // Cap'n Proto message.  This also applies to parseObject below.
     kj::Vector<Orphan<JsonValue>> values;
     auto orphanage = Orphanage::getForMessageContaining(output);