Add text-ranking pipeline tag

This PR adds the `text-ranking` pipeline tag to the model card, ensuring the model is correctly categorized and discoverable on the Hugging Face Hub. This improves the searchability and discoverability of the model.

README.md

@@ -1,8 +1,9 @@
 ---
-library_name: transformers
-license: mit
 base_model:
 - google/gemma-2-2b-it
+library_name: transformers
+license: mit
+pipeline_tag: text-ranking
 ---
 
 # R<sup>2</sup>ec: Towards Large Recommender Models with Reasoning
@@ -10,8 +11,6 @@ base_model:
 R<sup>2</sup>ec is a large recommender model with reasoning, generating both natural language rationales and ranked item predictions. 
 The model is fine-tuned with reinforcement learning to enhance its reasoning capabilities for more effective recommendations.
 
- 
-
 <p align="center">
   <a href="https://arxiv.org/pdf/2505.16994"><b>Paper Link</b>👁️</a>
 </p>