rectify docu

Device/Detector/SimulationAreaIterator.h

@@ -47,7 +47,7 @@ public:
 private:
     size_t nextIndex(size_t currentIndex);
     const SimulationArea* m_area;
-    size_t m_index;         //!< global index in detector plane defined by its axes
+    size_t m_index;         //!< ROI related index
     size_t m_element_index; //!< sequential number for SimulationElementVector
 };