Add `library_name` metadata tag

This PR improves the model card by adding the `library_name: transformers` tag to the metadata. This will enable the automatic display of a code snippet for using the model with the 🤗 Transformers library, making it easier for users to get started.

The model's `config.json` indicates compatibility with `GPT2LMHeadModel` and `transformers_version: "4.42.0.dev0"`, confirming its integration with the library.

README.md

@@ -1,15 +1,17 @@
 ---
-license: apache-2.0
+base_model:
+- openai-community/gpt2-xl
 datasets:
 - databricks/databricks-dolly-15k
 language:
 - en
+license: apache-2.0
 metrics:
 - rouge
-base_model:
-- openai-community/gpt2-xl
 pipeline_tag: text-generation
+library_name: transformers
 ---
+
 # teacher-gpt2-1.5B
 
 [paper](https://arxiv.org/abs/2306.08543) | [code](https://github.com/microsoft/LMOps/tree/main/minillm)