Add pipeline tag

This PR improves the model card by adding the `pipeline_tag: feature-extraction` to the metadata. This tag will help users discover BrainOmni when filtering models by task on the Hugging Face Hub, making it more accessible and visible to the community.

README.md

@@ -1,6 +1,8 @@
 ---
 license: mit
+pipeline_tag: feature-extraction
 ---
+
 # BrainOmni 🧠
 
 <div align="center">
@@ -37,4 +39,4 @@ If you use BrainOmni model or code, please cite the following paper:
 
 > Qinfan Xiao, Ziyun Cui, Chi Zhang, Siqi Chen, Wen Wu, Andrew Thwaites, Alexandra Woolgar,
 Bowen Zhou, Chao Zhang (2025) BrainOmni: A Brain Foundation Model for Unified EEG and MEG Signals,
-_arXiv_, [https://arxiv.org/abs/2505.18185](https://arxiv.org/abs/2505.18185)
+_arXiv_, [https://arxiv.org/abs/2505.18185](https://arxiv.org/abs/2505.18185)