Update model tags to make the model more discoverable

Hi there!
I've been looking for German summarization models recently, and only came across your fine-tuned model by accident.
The updates should make it more discoverable, since it is now possible to filter both for *"German*", as well as adding it to the *"summarization"* subset of models.

Best,
Dennis

README.md

@@ -2,8 +2,10 @@
 license: apache-2.0
 tags:
 - generated_from_trainer
+- summarization
 datasets:
 - mlsum
+language: de
 metrics:
 - rouge
 model-index: