Adding comment in Hovercard that we support cumulative area chart cur…

…rently (microsoft#29395)

* Adding comment in Hovercard that we support cumulative area chart currently

* change file

* Fixing review comments

* Fixing build failure

* Fixing review comment

* Resolving review comments

* Resolving review comments

packages/react-examples/src/react-charting/AreaChart/AreaChart.DataChange.Example.tsx

@@ -99,6 +99,10 @@ export class AreaChartDataChangeExample extends React.Component<{}, IAreaChartBa
  }}
  enableReflow={true}
  />
+ <div style={{ marginBottom: '13px' }}>
+ Note: Y values in callout display individual values. Y value plotted on chart are cumulative for the
+ datapoint.
+ </div>
  <DefaultButton text="Change Ydata" onClick={this._changeData} />
  <DefaultButton text="Change Xdata" onClick={this._changeXData} />
  </div>