人力车/ d3.js添加轴标题

Question

有没有办法为轴添加标题？通常，具有y轴显示单元是有用的。例如：http://code.shutterstock.com/rickshaw/examples/y_axis.html只有数字，但在任何类型的情节中你需要指定：％，$，km / s等。如何做到这一点？

谢谢！

var graph = new Rickshaw.Graph( {
    element: document.getElementById("chart"),
    renderer: 'line',
    height: 300,
    width: 800,
    series: [
        {
            data: [ { x: 0, y: 120 }, { x: 1, y: 890 }, { x: 2, y: 38 }, { x: 3, y: 70 }, { x: 4, y: 32 } ],
            color: "#c05020"
        }, {
            data: [ { x: 0, y: 80 }, { x: 1, y: 200 }, { x: 2, y: 100 }, { x: 3, y: 520 }, { x: 4, y: 133 } ],
            color: "#30c020"
        }, {
            data: [ { x: 0, y: 200 }, { x: 1, y: 390 }, { x: 2, y: 1000 }, { x: 3, y: 200 }, { x: 4, y: 230 } ],
            color: "#6060c0"
        }
    ]
} );

var y_ticks = new Rickshaw.Graph.Axis.Y( {
    graph: graph,
    orientation: 'left',
    tickFormat: Rickshaw.Fixtures.Number.formatKMBT,
    element: document.getElementById('y_axis'),
} );

graph.render();