Add some metadata to the model card

Hello!

## Pull Request overview
* Add `transformers` tag
* Add `text-generation` pipeline tag

## Details
These should make it a tad easier to find this model.

Also, as a heads up, in my experience, a small snippet in the model card with usage is often recommended to get people a good feel of what your model does, e.g.:
```python
rag = RAGWithCitations("PleIAs/Pleias-RAG-1B")

# Define query and sources
query = "What is the capital of France?"
sources = [
{
"text": "Paris is the capital and most populous city of France.",
"metadata": {"source": "Geographic Encyclopedia", "reliability": "high"}
},
{
"text": "The Eiffel Tower is located in Paris, France.",
"metadata": {"source": "Travel Guide", "year": 2020}
}
]

# Generate a response
response = rag.generate(query, sources)

# Print the final answer with citations
print(response["processed"]["clean_answer"])
```

(Except also include the import & printed output)

- Tom Aarsen

README.md

@@ -8,6 +8,9 @@ language:
 - es
 base_model:
 - PleIAs/Pleias-1.2B-Preview
+pipeline_tag: text-generation
+tags:
+- transformers
 ---