Update model metadata to set pipeline tag to the new `text-ranking`

Hello!

## Pull Request overview
* Update metadata to set pipeline tag to the new `text-ranking`

## Changes
This is an automated pull request to update the metadata of the model card. We recently introduced the [`text-ranking`](https://huggingface.co/models?pipeline_tag=text-ranking) pipeline tag for models that are used for ranking tasks, and we have a suspicion that this model is one of them.

Feel free to respond if you have questions or concerns.

- Tom Aarsen

README.md

@@ -7,6 +7,7 @@ tags:
 - finance
 - chemistry
 - biology
+pipeline_tag: text-ranking
 ---
 ![BGE-reranking](https://miro.medium.com/v2/resize:fit:4800/format:webp/1*tCBbIjV_jLZP1AKLTX7rAw.png)