添加 -d 指定数据集时错误提示 (#741)

* 添加 -d 指定数据集时错误提示

Warning: you do not have any of the recognized datasets in G:\AI\Dataset\aidatatang_200zh\aidatatang_200zh 
Please note use 'E:\datasets' as root path instead of 'E:\datasetsidatatang_200zh\corpus/test' as a example .
The recognized datasets are:

* Update ui.py

* Update ui.py

toolbox/ui.py

@@ -274,7 +274,9 @@ class UI(QDialog):
             if datasets_root is None or len(datasets) == 0:
                 msg = "Warning: you d" + ("id not pass a root directory for datasets as argument" \
                     if datasets_root is None else "o not have any of the recognized datasets" \
-                                                  " in %s" % datasets_root) 
+                                                  " in %s \n" \
+                                                  "Please note use 'E:\datasets' as root path " \
+                                                  "instead of 'E:\datasets\aidatatang_200zh\corpus\test' as an example "   % datasets_root) 
                 self.log(msg)
                 msg += ".\nThe recognized datasets are:\n\t%s\nFeel free to add your own. You " \
                        "can still use the toolbox by recording samples yourself." % \