feat(CardSubtitle): create new component

src/Card/CardSubtitle.js

@@ -0,0 +1,17 @@
+import React, { PropTypes } from 'react';
+import classnames from 'classnames';
+
+const propTypes = {
+  className: PropTypes.string,
+  children: PropTypes.node,
+};
+
+const CardSubtitle = ({ className, children }) => (
+  <h2
+    className={classnames('mdc-card__subtitle', className)}
+  >
+    {children}
+  </h2>
+  );
+CardSubtitle.propTypes = propTypes;
+export default CardSubtitle;

src/Card/index.js

@@ -3,3 +3,4 @@ import '@material/card/dist/mdc.card.min.css';
 export { default } from './Card';
 export { CardHeader } from './CardHeader';
 export { CardTitle } from './CardTitle';
+export { CardSubTitle } from './CardSubtitle';