add comment to 'determine_sweeps' method

pyart/util/radar_utils.py

@@ -172,6 +172,9 @@ def determine_sweeps(radar,
             sweep_start_index.append(t)
         t += 1
     sweep_number = np.arange(len(sweep_start_index))
+
+    # Update radar object
+    # ======================
     radar.sweep_start_ray_index['data'] = ma.array(sweep_start_index, dtype='int32')
     radar.sweep_end_ray_index['data'] = ma.array(sweep_end_index, dtype='int32')
     radar.sweep_number['data'] = ma.array(sweep_number, dtype='int32')