RF: return back indexes in comments for seqinfo_fields

They were originally introduced (and then removed without reasoning in
e529f5a) to make it easier to grasp what
fields some heuristics, accessing them by indexes, are interested in.  I would
prefer to keep them.  Also minimizes the diff for the PR

Author: yarikoptic

heudiconv/utils.py

@@ -21,28 +21,28 @@
 
 
 seqinfo_fields = [
-    'total_files_till_now',
-    'example_dcm_file',
-    'series_id',
-    'dcm_dir_name',
-    'series_files',
-    'unspecified',
-    'dim1', 'dim2', 'dim3', 'dim4',
-    'TR', 'TE',
-    'protocol_name',
-    'is_motion_corrected',
-    'is_derived',
-    'patient_id',
-    'study_description',
-    'referring_physician_name',
-    'series_description',
-    'sequence_name',
-    'image_type',
-    'accession_number',
-    'patient_age',
-    'patient_sex',
-    'date',
-    'series_uid',
+    'total_files_till_now',  # 0
+    'example_dcm_file',      # 1
+    'series_id',             # 2
+    'dcm_dir_name',          # 3
+    'series_files',          # 4
+    'unspecified',           # 5
+    'dim1', 'dim2', 'dim3', 'dim4', # 6, 7, 8, 9
+    'TR', 'TE',              # 10, 11
+    'protocol_name',         # 12
+    'is_motion_corrected',   # 13
+    'is_derived',            # 14
+    'patient_id',            # 15
+    'study_description',     # 16
+    'referring_physician_name', # 17
+    'series_description',    # 18
+    'sequence_name',         # 19
+    'image_type',            # 20
+    'accession_number',      # 21
+    'patient_age',           # 22
+    'patient_sex',           # 23
+    'date',                  # 24
+    'series_uid',            # 25
  ]
 
 SeqInfo = namedtuple('SeqInfo', seqinfo_fields)