Add alert function to AppView story

src/components/AppView/AppView.stories.mdx

@@ -20,7 +20,7 @@ export const Template = (args) => <AppView {...args} />
 <Canvas>
     <Story name="Default" 
         args={{
-            setDarkMode: () => alert("Function not set for docs."),
+            setDarkMode: _ => alert("Use the darkmode toggle in the toolbar above.")
         }}
     >
         {args => <AppView {...args} />}