Adding `transformers` as the library name

I see that vLLM deployment is possible and it should work OOTB with transformers. Merging this would help with more accurate downloads and also code snippet boxes.

README.md

@@ -1,6 +1,7 @@
 ---
 pipeline_tag: text-generation
 license: mit
+library_name: transformers
 ---
 
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