add last minute tweaks found while writing docs

imports/ui/components/Icon/Icon.js

@@ -0,0 +1,10 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+
+const Icon = ({ icon }) => (<i className={`fa fa-${icon}`} />);
+
+Icon.propTypes = {
+  icon: PropTypes.string.isRequired,
+};
+
+export default Icon;