Add task tag to enable widget

See docs: https://huggingface.co/docs/hub/models-widgets#enabling-a-widget

README.md

@@ -20,6 +20,7 @@ tags:
   - deberta
   - deberta-v3
   - mdeberta
+  - fill-mask
 thumbnail: https://huggingface.co/front/thumbnails/microsoft.png
 license: mit
 ---