Update README.md

Author: tschelabaumann

README.md

@@ -120,6 +120,9 @@ You may delete objects by calling the service's delete() method with an object i
 
 ## Changelog
 
+### 2.4.0
+* Add param client_id to checksum create function
+
 ### 2.3.0
 * Disable httplib debugging by default
 * http_debugging_enabled otional parameter added to PaymillContext