Update exercise0/storybook with an answer file

exercise0-storybook/README.md

@@ -13,3 +13,9 @@ yarn storybook
 Using the `ListingExcerpt.stories.jsx` file as a reference, create a
 new story in the same directory for the `DropdownList` component.
 It can be imported from the same directory as the `ListingExcerpt`.
+
+You can peek at the answer in `answer/DropdownList.stories-test.jsx`. Be sure to
+update the filename to exclude `-test` for it to show up in Storybook.
+
+Once you have a story for the DropdownList component, you can do some manual testing
+in isolation and make accessibility improvements to it.

exercise0-storybook/answer/DropdownList.stories-test.jsx

@@ -0,0 +1,19 @@
+import React from 'react';
+
+import DropdownList from 'components/dropdown-list';
+
+export default {
+  title: 'Components/DropdownList',
+  component: DropdownList,
+}
+
+// We create a “template” of how args map to rendering
+const Template = (args) => <DropdownList {...args} />;
+
+// Each story then reuses that template
+export const Default = Template.bind({});
+
+Default.args = {
+  defaultItemText: 'Fruits',
+  items: ['apples', 'pears', 'plums']
+};