title: Using chartjs-plugin-annotation with ng2-charts
body: <p>Using charts.js, chartjs-plugin-annotations and ng2-charts in angular 2 project, I need to annotate a line chart with a box annotation as in the figure bellow.
  <a href="https://i.stack.imgur.com/Wk9f1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Wk9f1.png" alt="enter image description here"></a></p>
  
  <p>Everything seems fine, except of the box annotations (red) that do not appear on the chart.
  The annotation related code are placed in chart options</p>
  
  <pre><code>annotation: {
       drawTime: 'beforeDatasetsDraw',
       annotations: [
          {
          type: 'box',
          id: 'y-axis-box',
          //mode: 'horizontal',
          yScaleID: 'y-axis-0',
          yMax: 2,
          yMin: 0,
          backgroundColor: 'red',
          //value: date,
          borderWidth: 2
          },
        {
          type: 'box',
          id: 'y-axis-1',
          //mode: 'horizontal',
          yScaleID: 'y-axis-0',
          yMax: 5,
          yMin: 4,
          backgroundColor: 'red',
          //value: date,
          borderWidth: 2
          }
      ]
    }
  </code></pre>
  
  <p>It appear that some extra configuration is required, mainly registering the plugin. The charts is drown using the baseChart directive from the imported ChartsModule in app.module.js</p>
  
  <pre><code>import {ChartsModule} from 'ng2-charts/ng2-charts';
  </code></pre>