doc: document starpu_task_wait_array()

doc/doxygen/chapters/api/codelet_and_tasks.doxy

@@ -769,6 +769,12 @@ to wait for synchronous or detached tasks. Upon successful completion,
 this function returns 0. Otherwise, <c>-EINVAL</c> indicates that the
 specified task was either synchronous or detached.
 
+\fn int starpu_task_wait_array(struct starpu_task **tasks, unsigned nb_tasks)
+\ingroup API_Codelet_And_Tasks
+This function allows to wait for an array of tasks. Upon successful completion,
+this function returns 0. Otherwise, <c>-EINVAL</c> indicates that a task
+was either synchronous or detached.
+
 \fn int starpu_task_submit(struct starpu_task *task)
 \ingroup API_Codelet_And_Tasks
 This function submits task to StarPU. Calling this function