add `library_name=transformers` tag for deploy button to display

https://discuss.huggingface.co/t/deploy-button-not-showing-fine-tuned-llama-3-1/103630/2

README.md

@@ -4,6 +4,7 @@ inference: true
 license: apache-2.0
 datasets:
 - simplescaling/s1K
+library_name: transformers
 ---
 
 # Model Summary