Update model card

This PR updates the model card with the correct `pipeline_tag` (`question-generation`) and adds the `library_name` metadata tag to ensure users know which library it is compatible with. It also adds a link to the code repository.

README.md

@@ -1,9 +1,11 @@
 ---
-license: apache-2.0
-language:
-- en
 base_model:
 - facebook/bart-large
+language:
+- en
+license: apache-2.0
+library_name: pytorch
+pipeline_tag: question-generation
 ---
 
 > This Question Generation model is a part of the [PlainQAFact](https://github.com/zhiwenyou103/PlainQAFact) factuality evaluation framework. 
@@ -68,4 +70,6 @@ If you use this QG model in your research, please cite with the following BibTex
       primaryClass={cs.CL},
       url={https://arxiv.org/abs/2503.08890}, 
 }
-```
+```
+
+Code: https://github.com/zhiwenyou103/PlainQAFact