Add library_name: transformers to metadata

This PR improves the model card by adding the `library_name: transformers` metadata tag.

This change is based on evidence from the `config.json` (`"architectures": ["VibeVoiceForConditionalGeneration"]`, `"transformers_version": "4.51.3"`) and `preprocessor_config.json` (`"processor_class": "VibeVoiceProcessor"`), indicating compatibility with the `transformers` library. Adding this tag will enable the automated "how to use" widget on the model page, making it easier for users to interact with the model.

No other changes are made, as the existing paper, code, and project page links are accurate, and no `transformers` Python sample usage was explicitly found in the GitHub README.

README.md

@@ -1,11 +1,12 @@
 ---
-license: mit
 language:
 - en
 - zh
+license: mit
 pipeline_tag: text-to-speech
 tags:
 - Podcast
+library_name: transformers
 ---
 
 ## VibeVoice: A Frontier Open-Source Text-to-Speech Model