Actually add the tooltip. Oops.

app/components/common/Tooltip.js

@@ -0,0 +1,25 @@
+import React, { Component } from 'react';
+
+import PropTypes from 'prop-types';
+import { Popup } from 'semantic-ui-react';
+
+export default class Tooltip extends Component {
+  static propTypes = {
+    children: PropTypes.any.isRequired,
+    title: PropTypes.string.isRequired,
+  };
+
+  render() {
+    const { title, children, ...rest } = this.props;
+    return (
+      <Popup
+        size="mini"
+        position="top center"
+        content={title}
+        inverted={true}
+        trigger={children}
+        {...rest}
+      />
+    );
+  }
+}