Add task category and language tag

This PR adds the `task_categories` and `language` fields to the dataset card to improve discoverability.

README.md

@@ -43,7 +43,12 @@ configs:
     path: data/train-*
   - split: test
     path: data/test-*
+task_categories:
+- image-classification
+language:
+- en
 ---
+
 ## Citation
 
 ```bibtex