update readme

Author: benweizhu

README.md

@@ -1 +1,46 @@
-# react-heatmap
+# react-heatmap
+
+A React Component based on [heatmap.js][b7fa289f].
+
+  [b7fa289f]: https://www.patrick-wied.at/static/heatmapjs/ "heatmap.js"
+
+```
+import React from 'react';
+import ReactDom from 'react-dom';
+import ReactHeatmap from 'react-heatmap';
+
+class ReactHeatmapExample extends React.Component {
+  render() {
+    var points = [];
+    var max = 0;
+    var width = 840;
+    var height = 400;
+    var len = 300;
+
+    while (len--) {
+      var val = Math.floor(Math.random() * 100);
+      // now also with custom radius
+      var radius = Math.floor(Math.random() * 70);
+
+      max = Math.max(max, val);
+      var point = {
+        x: Math.floor(Math.random() * width),
+        y: Math.floor(Math.random() * height),
+        value: val,
+        // radius configuration on point basis
+        radius: radius
+      };
+      points.push(point);
+    }
+
+    return (
+      <div style={{ width: '840px', height: '400px' }}>
+        < ReactHeatmap max= { max } data= { points } unit= "notPercent" />
+      </div >
+    );
+  }
+}
+
+ReactDom.render(<ReactHeatmapExample />, document.querySelector('#app'));
+
+```