!271 Fix repeat and epoch api notice discription

Merge pull request !271 from pengyanjun/fix_repeat_epoch_doc

mindspore/dataset/engine/datasets.py

@@ -394,6 +394,8 @@ class Dataset:
             The order of using repeat and batch reflects the number of batches. Recommend that
             repeat operation should be used after batch operation.
             If dataset_sink_mode is False, here repeat operation is invalid.
+            If dataset_sink_mode is True, repeat count should be euqal to the epoch of training. Otherwise,
+            errors could occur since the amount of data is not the amount training requires.
 
         Args:
             count (int): Number of times the dataset should be repeated (default=None).

mindspore/train/model.py

@@ -362,6 +362,9 @@ class Model:
 
         Note:
             CPU is not supported when dataset_sink_mode is true.
+            If dataset_sink_mode is True, epoch of training should be equal to the count of repeat
+            operation in dataset processing. Otherwise, errors could occur since the amount of data
+            is not the amount training requires.
 
         Args:
             epoch (int): Total number of iterations on the data.