Update switch.md

Add documentation for thumb named slot

apps/www/src/content/docs/components/switch.md

@@ -47,6 +47,18 @@ import { Switch } from '@/components/ui/switch'
   <Switch />
 </template>
 ```
+# Add icon inside switch thumb
+
+```vue
+<template>
+  <Switch :checked="isDark" @update:checked="toggleTheme">
+      <template #thumb>
+          <Icon v-if="isDark" icon="lucide:moon" class="size-3"></Icon>
+          <Icon v-else icon="lucide:sun" class="size-3"></Icon>
+      </template>
+  </Switch>
+</template>
+```
 
 ## Examples