message: doc: add entity cluster example
diff: import React from "react";
  -import { Cartesian3, Color } from "cesium";
  +import { Cartesian3, Color, EntityCluster } from "cesium";
  import { storiesOf } from "@storybook/react";
  import Viewer from "../Viewer";
  @@ -7,7 +7,8 @@ import CustomDataSource from "../CustomDataSource";
  import Entity from "../Entity";
  export default () => {
  - storiesOf("CustomDataSource", module).add("default", () => (
  + storiesOf("CustomDataSource", module)
  + .add("default", () => (
  <Viewer full>
  <CustomDataSource name="custom">
  <Entity
  @@ -32,5 +33,30 @@ export default () => {
  point={{ pixelSize: 10 }}
  />
  </Viewer>
  + ))
  + .add("entity clustering", () => (
  + <Viewer full>
  + <CustomDataSource
  + clustering={
  + new EntityCluster({
  + enabled: true,
  + pixelRange: 50,
  + minimumClusterSize: 3,
  + clusterPoints: true,
  + })
  + }>
  + {new Array(100).fill(0).map((_, i) => (
  + <Entity
  + key={i}
  + position={Cartesian3.fromDegrees(
  + Math.random() * 180 - 90,
  + Math.random() * 360 - 180,
  + 100,
  + )}
  + point={{ pixelSize: 10, color: Color.RED }}
  + />
  + ))}
  + </CustomDataSource>
  + </Viewer>
  ));
  };
  