Update API.md "Customizable Initial Validation"

Author: Huei Tan

API.md

@@ -289,3 +289,13 @@ angular.module('yourApp', ['validation'])
     }]);
 ```
 
+### **Customizable Initial Validation**<br/>
+Intial Validation for the input false. You can make it to true!
+
+```html
+<!-- default fase -->
+<input type="text" name="firstName" ng-model="firstName" validator="required"/>
+
+<!-- set to true -->
+<input type="text" name="firstName" ng-model="firstName" validator="required" initial-validity="true"/>
+```