Add library_name: transformers to metadata

This PR adds `library_name: transformers` to the model card metadata. This enables the "Use in Transformers" button on the model page, as the model is compatible with the `transformers` library via the `auto_map` configuration in its `config.json`. The rest of the metadata and the model card content have been preserved.

README.md

@@ -1,10 +1,12 @@
 ---
-language:
-- en
 base_model:
 - GSAI-ML/LLaDA-8B-Base
+language:
+- en
 pipeline_tag: text-generation
+library_name: transformers
 ---
+
 ## Edit-Based Refinement for Parallel Masked Diffusion Language Models
 
 <p align="center">