Add the storybook story for the CustomGradientPicker component

packages/components/src/custom-gradient-picker/stories/index.js

@@ -0,0 +1,29 @@
+/**
+ * WordPress dependencies
+ */
+import { useState } from '@wordpress/element';
+
+/**
+ * Internal dependencies
+ */
+import CustomGradientPicker from '../';
+
+export default {
+	title: 'Components/CustomGradientPicker',
+	component: CustomGradientPicker,
+};
+
+const CustomGradientPickerWithState = ( props ) => {
+	const [ gradient, setGradient ] = useState();
+	return (
+		<CustomGradientPicker
+			{ ...props }
+			value={ gradient }
+			onChange={ setGradient }
+		/>
+	);
+};
+
+export const _default = () => {
+	return <CustomGradientPickerWithState />;
+};