echarts如何添加指示線？

option = {

tooltip: {
    trigger: 'item',
    formatter: "{a} <br/>: {c} (lvvt1tz%)"
},
legend: {
    orient: 'vertical',
    x: 'left',
    data:['直接訪問(wèn)','郵件營(yíng)銷','聯(lián)盟廣告','視頻廣告','搜索引擎']
},
series: [
    {
        name:'訪問(wèn)來(lái)源',
        type:'pie',
        radius: ['50%', '70%'],
        avoidLabelOverlap: false,
        label: {
            normal:{
                show:true,
                position:'center',
                formatter:function(){
                    return '20元'
                },
                textStyle:{
                    color:'green',
                    fontSize:40
                },
                labelLine:{
                  
                } 
            },
            labelLine: {
            normal: {
                show: true
            }
        },   
        },
        labelLine: {
            normal: {
                show: true
            }
        },
        data:[
            {value:335, name:'直接訪問(wèn)'},
            {value:310, name:'郵件營(yíng)銷'},
            {value:234, name:'聯(lián)盟廣告'},
            {value:135, name:'視頻廣告'},
            {value:1548, name:'搜索引擎'}
        ]
    }
]

};