add train/val split

README.md

@@ -134,7 +134,8 @@ topic_en:           The topics of the variable in English.
 
 | Split               | Number of sentences                       |
 | ------------------- | ------------------------------------      |
-| Train               | 4,248                                     |
+| Train               | 3,823                                     |
+| Validation          |   425                                     |
 
 ## Dataset Creation