Align desktop initializer arguments with builders

readme.md

@@ -33,21 +33,23 @@ loader glue. An application with no state beyond the UI state receives
 ```rust
 use iris::prelude::*;
 
+fn build<Rsc: UiRsc>(rsc: &mut Rsc, ui_state: &mut impl HasRoot<Rsc>) {
+    rect(PaintId::RED).set_root(rsc, ui_state);
+}
+
 #[iris::app_init]
 fn create(
     ui_state: &mut AndroidUiState,
     rsc: &mut StdRsc<AndroidUiState>,
 ) {
-    rect(PaintId::RED).set_root(rsc, ui_state);
+    build(rsc, ui_state);
 }
 ```
 
 Desktop has the corresponding initializer form:
 
 ```rust
-DesktopApp::<DesktopUiState>::run_with(|ui_state, rsc| {
-    rect(PaintId::RED).set_root(rsc, ui_state);
-});
+DesktopApp::<DesktopUiState>::run_with(build);
 ```
 
 Background work updates either host through the same task context. An update