!45959 update comment for ImageNetToMR api

Merge pull request !45959 from guozhijian/code_docs_imagenet_to_mr

docs/api/api_python/mindrecord/mindspore.mindrecord.ImageNetToMR.rst

@@ -4,7 +4,7 @@
     将ImageNet数据集转换为MindRecord格式数据集。
 
     参数：
-        - **map_file** (str) - 标签映射文件的路径。映射文件内容如下：
+        - **map_file** (str) - 标签映射文件的路径。该文件可通过命令： `ls -l [image_dir] | grep -vE "总用量|total|\." | awk -F " " '{print $9, NR-1;}' > [file_path]` 生成，其中 `image_dir` 为ImageNet数据集的目录路径， `file_path` 为生成的 `map_file` 文件 。 `map_file` 文件内容示例如下：
 
           .. code-block::
 

mindspore/python/mindspore/mindrecord/tools/imagenet_to_mr.py

@@ -27,11 +27,14 @@ __all__ = ['ImageNetToMR']
 
 
 class ImageNetToMR:
-    """
+    r"""
     A class to transform from imagenet to MindRecord.
 
     Args:
-        map_file (str): The map file that indicates label. The map file content should be like this:
+        map_file (str): The map file that indicates label. This file can be generated by command
+            `ls -l [image_dir] | grep -vE "total|\." | awk -F " " '{print $9, NR-1;}' > [file_path]` , where `image_dir`
+            is image directory contains n02119789, n02100735, n02110185 and n02096294 directory and `file_path` is
+            the generated `map_file` . An example of `map_file` is as below:
 
             .. code-block::