如何为amcharts地图添加标题？

<script src="https://www.amcharts.com/lib/4/core.js"></script>
<script src="https://www.amcharts.com/lib/4/maps.js"></script>
<script src="https://www.amcharts.com/lib/4/themes/animated.js"></script>
<link rel="stylesheet" href="https://www.amcharts.com/lib/4/maps.css" />

<div id="chartdiv"></div>

// 创建地图实例
var chart = am4core.create("chartdiv", am4maps.MapChart);

// 设置地图的数据源
chart.geodata = am4geodata_worldLow;

// 设置地图的投影方式
chart.projection = new am4maps.projections.Miller();

// 创建地图的多边形系列
var polygonSeries = chart.series.push(new am4maps.MapPolygonSeries());

// 设置多边形的数据源
polygonSeries.useGeodata = true;

// 创建地图的标题
var title = chart.titles.create();
title.text = "地图标题";
title.fontSize = 20;
title.marginBottom = 20;

// 渲染地图
chart.render();