update error print to say how many arguments are expected

Summary:
Current error message is unhelpful :(
add some context to how many arguments were expected

Reviewed By: chadaustin

Differential Revision: D64968870

fbshipit-source-id: d5bea38c5c5f0cbf87441da53db19f7e26fd9285

watchman/cmds/query.cpp

@@ -19,7 +19,7 @@ using namespace watchman;
 /* query /root {query} */
 static UntypedResponse cmd_query(Client* client, const json_ref& args) {
   if (json_array_size(args) != 3) {
-    throw ErrorResponse("wrong number of arguments for 'query'");
+    throw ErrorResponse("wrong number of arguments for 'query', expected 3");
   }
 
   auto root = resolveRoot(client, args);