add UpdateDocument to list of SearcherActor messages

how did this even work?!
I've only been using UpdateDocument so far, and it wasn't listed!

plume-models/src/search/searcher.rs

@@ -38,7 +38,7 @@ pub struct UpdateDocument(pub Post);
 #[derive(Clone, Debug)]
 pub struct DeleteDocument(Post);
 
-#[actor(AddDocument)]
+#[actor(AddDocument, UpdateDocument)]
 pub struct SearcherActor(Searcher);
 
 impl Actor for SearcherActor {