docs: add missing component slots

docs/content/3.forms/5.checkbox.md

@@ -95,6 +95,24 @@ props:
 ---
 ::
 
+## Slots
+
+### `label`
+
+Use the `#label` slot to override the content of the label.
+
+::component-card
+---
+slots:
+  label: <span class="italic">Label</span>
+baseProps:
+  name: 'checkbox5'
+---
+
+#label
+  [Label]{.italic}
+::
+
 ## Props
 
 :component-props