Update model metadata to set pipeline tag to the new `text-ranking` and tags to `sentence-transformers`

Hello!

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

## 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. I also updated added metadata to specify that this model can be loaded with the `sentence-transformers` library, as it should be possible to load any model compatible with `transformers` `AutoModelForSequenceClassification`.

Feel free to verify that it works with the following:

```bash
pip install sentence-transformers
```

```python
from sentence_transformers import CrossEncoder

model = CrossEncoder("rasyosef/roberta-amharic-reranker-medium")
scores = model.predict([
("How many people live in Berlin?", "Berlin had a population of 3,520,031 registered inhabitants in an area of 891.82 square kilometers."),
("How many people live in Berlin?", "Berlin is well known for its museums."),
])
print(scores)
```

Feel free to respond if you have questions or concerns.

- Tom Aarsen

README.md

@@ -2,10 +2,12 @@
 library_name: transformers
 tags:
 - cross-encoder
+- sentence-transformers
 language:
 - am
 base_model:
 - rasyosef/roberta-medium-amharic
+pipeline_tag: text-ranking
 ---
 
 # Cross-Encoder: roberta-amharic-reranker-medium