Add `library_name: transformers` to model card metadata

This PR enhances the model card by adding the `library_name: transformers` tag to the metadata. This is based on evidence from `config.json` (which shows `transformers_version` and `OPTForCausalLM` architecture) and `tokenizer_config.json` (which specifies `GPT2Tokenizer`). Adding this tag will enable the automated "how to use" widget on the Hugging Face Hub, providing users with a readily available and verified code snippet for model inference.

README.md

@@ -1,15 +1,17 @@
 ---
-license: apache-2.0
+base_model:
+- facebook/opt-6.7b
 datasets:
 - databricks/databricks-dolly-15k
 language:
 - en
+license: apache-2.0
 metrics:
 - rouge
-base_model:
-- facebook/opt-6.7b
 pipeline_tag: text-generation
+library_name: transformers
 ---
+
 # MiniLLM-OPT-6.7B
 
 [paper](https://arxiv.org/abs/2306.08543) | [code](https://github.com/microsoft/LMOps/tree/main/minillm)