Update README.md

The MiniCPM model is truly impressive! We would like to contribute by updating the README to include the base_model information. This is to address the missing details in the model card.

README.md

@@ -6,6 +6,8 @@ tags:
 - MiniCPM
 - ModelBest
 - THUNLP
+base_model:
+- openbmb/MiniCPM-2B-128k
 ---