Update README.md

Author: mike-schultz

README.md

@@ -111,13 +111,15 @@ Example :
 The ZingChart Component takes the following attributes:
 
 
-### _id_ [string] ```(required)```
+### _id_ [string] ```(optional)```
 The id for the DOM element for ZingChart to attach to.
 ##### Example:
 ```html
 <zingchart id="chart-1"></zingchart>
 ```
 
+If no id is specified, the id will be autogenerated in the form of `zingchart-auto-#`
+
 ---