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

@@ -1 +1,4 @@
+---
+pipeline_tag: text-ranking
+---
 This is model of Alibaba-NLP/gte-multilingual-reranker-base, revision "4e88bd5dec38b6b9a7e623755029fc124c319d67". Dicussion: [link](https://huggingface.co/Alibaba-NLP/gte-multilingual-reranker-base/discussions/12)