refactor docstring

Author: OutisLi

deepmd/utils/argcheck.py

@@ -3226,9 +3226,13 @@ def training_args(
         "of batches for system i and p_i is the sampling probability after "
         "sys_probs/auto_prob normalization. In multi-task mode, model_prob is "
         "normalized to sum to 1, per-task total_numb_batch values are computed "
-        "as above, and the final total_numb_batch is their model_prob-weighted "
-        "sum. At least one of numb_steps or num_epoch must be set; otherwise a "
-        "ValueError is raised."
+        "as above, and the final total_numb_batch is their model_prob-weighted sum. "
+        "Note that in multi-task mode, this defines an 'expected epoch' where each "
+        "sample is visited once in expectation across all tasks, rather than a "
+        "full epoch for each individual task. For multi-task pretraining scenarios "
+        "where different tasks require different numbers of visits, using numb_steps "
+        "directly is recommended for more explicit control. At least one of numb_steps "
+        "or num_epoch must be set; otherwise a ValueError is raised."
     )
     doc_seed = "The random seed for getting frames from the training data set."
     doc_disp_file = "The file for printing learning curve."