Add pipeline tag, library name, and clean up model card

This PR improves the model card by adding the `pipeline_tag` set to `text-generation` and `library_name: transformers` to the metadata. This ensures the model is properly categorized and enables the automated "how to use" widget on the Hugging Face Hub.

Additionally, redundant `

README.md

@@ -1,8 +1,11 @@
 ---
-license: mit
 language:
 - en
+license: mit
+pipeline_tag: text-generation
+library_name: transformers
 ---
+
 # PromptCoT-2.0-SelfPlay-4B
 
 This model is part of **PromptCoT 2.0** (*Scaling Prompt Synthesis for LLM Reasoning*).