Add model card

This PR creates a model card for the "CodeI/O: Condensing Reasoning Patterns via Code Input-Output Prediction" repository.
It ensures the model can be found at https://huggingface.co/models?pipeline_tag=text-generation.

README.md

@@ -1,7 +1,5 @@
 ---
-# For reference on dataset card metadata, see the spec: https://github.com/huggingface/hub-docs/blob/main/datasetcard.md?plain=1
-# Doc / guide: https://huggingface.co/docs/hub/datasets-cards
-{}
+pipeline_tag: text-generation
 ---
 
 # CodeI/O: Condensing Reasoning Patterns via Code Input-Output Prediction