putting back the comment which got removed accidently, no functionality change

scripts/chat_sft.py

@@ -293,6 +293,7 @@ def sft_data_generator_bos_bestfit(split, buffer_size=100):
         targets[mask_targets == 0] = -1
 
         # Mask out padding positions in targets (set to -1 = ignore_index)
+        # For each row, positions >= (content_length - 1) in targets should be masked
         for i, content_len in enumerate(row_lengths):
             if content_len < row_capacity:
                 targets[i, content_len-1:] = -1