feat(playground): Slack and Docs links

Author: paveltiunov

packages/cubejs-playground/src/App.js

@@ -1,11 +1,11 @@
-/* eslint-disable no-undef */
+/* eslint-disable no-undef,react/jsx-no-target-blank */
 import React, { Component } from 'react';
 import { Link } from "react-router-dom";
 import * as PropTypes from 'prop-types';
 import "antd/dist/antd.css";
 import "./index.css";
 import {
-  Layout, Menu, Alert, notification
+  Layout, Menu, Alert, notification, Icon
 } from "antd";
 import { fetch } from 'whatwg-fetch';
 import { withRouter } from "react-router";
@@ -82,6 +82,24 @@ class App extends Component {
             <Menu.Item key="/explore"><Link to="/explore">Explore</Link></Menu.Item>
             <Menu.Item key="/dashboard"><Link to="/dashboard">Dashboard</Link></Menu.Item>
             <Menu.Item key="/schema"><Link to="/schema">Schema</Link></Menu.Item>
+            <Menu.Item
+              key="docs"
+              style={{ float: 'right' }}
+            >
+              <a href="https://cube.dev/docs" target="_blank">
+                <Icon type="book" />
+                Docs
+              </a>
+            </Menu.Item>
+            <Menu.Item
+              key="slack"
+              style={{ float: 'right' }}
+            >
+              <a href="https://slack.cube.dev" target="_blank">
+                <Icon type="slack" />
+                Slack
+              </a>
+            </Menu.Item>
           </Menu>
         </Header>
         <Content style={{ height: '100%' }}>