fix mention of instruct model (we didnt tune on it)

README.md

@@ -24,7 +24,7 @@ We are excited to introduce Shuttle-2.5-mini, our next-generation state-of-the-a
 
 * **Model Name**: Shuttle-2.5-mini
 * **Developed by**: ShuttleAI Inc.
-* **Base Model**: [Mistral-Base-Instruct-2407](https://huggingface.co/mistralai/Mistral-Nemo-Base-2407)
+* **Base Model**: [Mistral-Base-Base-2407](https://huggingface.co/mistralai/Mistral-Nemo-Base-2407)
 * **Parameters**: 13B
 * **Language(s)**: Multilingual
 * **Repository**: [https://huggingface.co/shuttleai](https://huggingface.co/shuttleai)