docs: add missing submit slot info in AutoForm docs

Author: Norbiros

docs/content/2.customization/2.form.md

@@ -26,6 +26,7 @@ you want to provide submit or edit form feature.
 |-----------------|---------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------|
 | `before-fields` |                                                               | Slot inside [`<UForm>`](https://ui.nuxt.com/components/form) before the list of [`<UFormField>`](https://ui.nuxt.com/components/form-field) |
 | `after-fields`  |                                                               | Slot inside [`<UForm>`](https://ui.nuxt.com/components/form) after the list of [`<UFormField>`](https://ui.nuxt.com/components/form-field)  |
+| `submit`        | `{ disabled: boolean }`                                       | Slot for customizing the submit button. `disabled` indicates whether at least one field is invalid.                                         |
 | `<field>`       | `{ field: string, state: Ref<Record<string, any> }>`{lang=ts} | **Dynamic** slot for a specific field inside Zod schema.                                                                                    |
 
 ### Dynamic slots