docs: improve slots sections

docs/content/3.forms/3.select.md

@@ -180,6 +180,46 @@ excludedProps:
 ---
 ::
 
+## Slots
+
+### `leading`
+
+Use the `#leading` slot to set the content of the leading icon.
+
+::component-card
+---
+slots:
+  leading: <UAvatar src="https://avatars.githubusercontent.com/u/739984?v=4" size="3xs" />
+baseProps:
+  name: 'select'
+  options:
+    - 'United States'
+    - 'Canada'
+    - 'Mexico'
+  placeholder: 'Search...'
+---
+
+#leading
+  :u-avatar{src="https://avatars.githubusercontent.com/u/739984?v=4" size="3xs"}
+::
+
+### `trailing`
+
+Use the `#trailing` slot to set the content of the trailing icon.
+
+::component-card
+---
+slots:
+  trailing: <UIcon name="i-heroicons-arrows-up-down-20-solid" />
+baseProps:
+  name: 'input'
+  placeholder: 'Search...'
+---
+
+#trailing
+  :u-icon{name="i-heroicons-arrows-up-down-20-solid"}
+::
+
 ## Props
 
 :component-props