ChangeLog: mention prolog callback introduced in #11012

ChangeLog

@@ -47,6 +47,9 @@ New features:
     _STARPU_PERFMODEL_VERSION should be updated. It is then possible
     to switch easily between differents versions of StarPU having
     different performance model formats.
+  * Tasks can now define a optional prolog callback which is executed
+    on the host just before the task is pushed. Tasks which depend on
+    the task might already be executing.
 
 Small features:
   * Add cl_arg_free field to enable automatic free(cl_arg) on task