Add paper link, correct pipeline tag

This PR adds a link to the paper page, and ensures the pipeline tag is correct, ensuring people can find it at https://huggingface.co./models?pipeline_tag=text-generation.

README.md

@@ -9,11 +9,9 @@ tags:
 model-index:
 - name: GuardReasoner 3B
   results: []
+pipeline_tag: text-generation
 ---
 
-
 # GuardReasoner 3B
 
-This model is a fine-tuned version of [meta-llama/Llama-3.2-3B](https://huggingface.co/meta-llama/Llama-3.2-3B) via R-SFT and HS-DPO.
-
-
+This model is a fine-tuned version of [meta-llama/Llama-3.2-3B](https://huggingface.co/meta-llama/Llama-3.2-3B) via R-SFT and HS-DPO, as described in [GuardReasoner: Towards Reasoning-based LLM Safeguards](https://huggingface.co/papers/2501.18492).