feat(textarea): add textarea to storybook

docs/textarea.stories.js

@@ -0,0 +1,18 @@
+import { storiesOf } from '@storybook/html'; // eslint-disable-line import/no-extraneous-dependencies
+import { // eslint-disable-line import/no-extraneous-dependencies
+  withKnobs, radios,
+} from '@storybook/addon-knobs';
+
+const stories = storiesOf('Textareas', module);
+stories.addDecorator(withKnobs);
+
+stories.add('textarea', () => {
+  const selectedClass = radios('class', {
+    default: '',
+    'is-success': 'is-success',
+    'is-warning': 'is-warning',
+    'is-error': 'is-error',
+  }, '');
+
+  return `<textarea id="textarea_field" class="textarea ${selectedClass}" placeholder="NES.css">`;
+});