Add missing variants to README.md (#2769)

Author: hacknug

packages/@headlessui-tailwindcss/README.md

@@ -39,13 +39,14 @@ module.exports = {
 Use Tailwind CSS utilities for styling the components based on their state. You can use the
 following variants:
 
-| Variant       | Inverse variant   |
-| ------------- | ----------------- |
-| `ui-open`     | `ui-not-open`     |
-| `ui-checked`  | `ui-not-checked`  |
-| `ui-selected` | `ui-not-selected` |
-| `ui-active`   | `ui-not-active`   |
-| `ui-disabled` | `ui-not-disabled` |
+| Variant            | Inverse variant        |
+| ------------------ | ---------------------- |
+| `ui-open`          | `ui-not-open`          |
+| `ui-checked`       | `ui-not-checked`       |
+| `ui-selected`      | `ui-not-selected`      |
+| `ui-active`        | `ui-not-active`        |
+| `ui-disabled`      | `ui-not-disabled`      |
+| `ui-focus-visible` | `ui-not-focus-visible` |
 
 Example: