docs: improve slots sections

docs/content/2.elements/3.button.md

@@ -275,6 +275,48 @@ code: |
 :u-button{icon="i-heroicons-chevron-down-20-solid" color="gray"}
 ::
 
+## 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:
+  color: 'gray'
+props:
+  label: Button
+  color: 'gray'
+excludedProps:
+  - color
+---
+
+#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-arrow-right-20-solid" />
+props:
+  label: Button
+  color: 'gray'
+excludedProps:
+  - color
+---
+
+#trailing
+  :u-icon{name="i-heroicons-arrow-right-20-solid"}
+::
+
 ## Props
 
 :component-props