Update README.md (add a link to Mistral)

Same as [the update for Swallow-MX-8x7b-NVE-v0.1](https://huggingface.co/tokyotech-llm/Swallow-MX-8x7b-NVE-v0.1/discussions/1) - just adding a link to the original model.
Thanks for the review!🤗

README.md

@@ -10,7 +10,7 @@ license: apache-2.0
 
 # Swallow-MS-7b-v0.1
 
-Our Swallow-MS-7b-v0.1 model has undergone continuous pre-training from the Mistral-7B-v0.1, primarily with the addition of Japanese language data. **The instruction tuning version will be released soon.**
+Our Swallow-MS-7b-v0.1 model has undergone continuous pre-training from the [Mistral-7B-v0.1](https://huggingface.co/mistralai/Mistral-7B-v0.1), primarily with the addition of Japanese language data. **The instruction tuning version will be released soon.**
 
 ![logo](./logo.png)