add minimal example

examples/minimal.rs

@@ -0,0 +1,20 @@
+use iris::{prelude::*, winit::*};
+
+struct State {
+    ui: DefaultUi,
+}
+
+fn main() {
+    UiApp::<State>::run();
+}
+
+impl DefaultUiState for State {
+    fn new(mut ui: DefaultUi, _proxy: Proxy<Self::Event>) -> Self {
+        rect(Color::RED).set_root(&mut ui);
+        Self { ui }
+    }
+
+    fn ui(&mut self) -> &mut DefaultUi {
+        &mut self.ui
+    }
+}