Update README.md

Congratulations on the impressive work with SeaLLM-7B-v2.5! We would love to contribute by updating the README to include the base model information. This will help address the current gap in the model card.

README.md

@@ -16,6 +16,8 @@ language:
 tags:
 - multilingual
 - sea
+base_model:
+- google/gemma-7b
 ---
 
 <p align="center">