replace json image to code block

Author: incandescentxxc

README.md

@@ -100,7 +100,28 @@ public static void main(String[] args) {
     String jsonStr = engine.renderJsonOption(lineChart);
 }
 ```
-<img src="assets/imgs/renderJsonOption.png" alt="Json Representation" style="width:95%;" />
+
+The output JSON object will be like the following,
+
+```json
+{
+  "xAxis": [
+    {
+      "type": "category",
+      "data": ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"],
+      "boundaryGap": false
+    }
+  ],
+  "yAxis": [{ "type": "value" }],
+  "series": [
+    {
+      "type": "line",
+      "data": [820, 932, 901, 934, 1290, 1330, 1320],
+      "areaStyle": {}
+    }
+  ]
+}
+```
 
 ### Integrate with Spring Web Application