updated README.MD - link to api documentation

Author: torkvell

README.MD

@@ -29,7 +29,7 @@ It makes use of the API to request the following products and resources:
 - Campaigns
 - Campaign results
 
-For more information on resources, authorization and available API calls, please visit our [documentation](https://usabilla.com/api).
+For more information on resources, authorization and available API calls, please visit our [documentation](https://developers.usabilla.com).
 
 ## Installation: