move au into nu/render

src/main.zig

@@ -5,7 +5,10 @@ const App = @import("App.zig");
 
 pub const nu_options: nu.Options = .{
     .window = .{ .title = "Hello World" },
-    .render = .{ .app_name = "hello-world" },
+    .render = .{
+        .app_name = "hello-world",
+        .frames_in_flight = 3,
+    },
 };
 
 pub fn main() !void {