!3540 [MD]fix error message when file exists.

Merge pull request !3540 from liyong126/fix_mindrecord_log

mindspore/ccsrc/minddata/mindrecord/io/shard_writer.cc

@@ -83,7 +83,7 @@ MSRStatus ShardWriter::OpenDataFiles(bool append) {
       // if not append and mindrecord file exist, return FAILED
       fs->open(common::SafeCStr(file), std::ios::in | std::ios::binary);
       if (fs->good()) {
-        MS_LOG(ERROR) << "MindRecord file already existed.";
+        MS_LOG(ERROR) << "MindRecord file already existed, please delete file: " << common::SafeCStr(file);
         fs->close();
         return FAILED;
       }

mindspore/dataset/engine/datasets.py

@@ -1082,7 +1082,7 @@ class Dataset:
              - None
              - Not support
            * - DE_FLOAT16
-             - float32
+             - Not support
              -
            * - DE_FLOAT32
              - float32