update license in readme.md

Hi, I'm Chen, a DevRel specialist from 01.AI.
Today I'm sending you the PR to help you update the model license, and give a recommendation according to apache-2.0.
1. License Update:
Since license of all Yi Series models has been updated from yi-license to apache-2.0, this PR is to help you update it.
License under apache-2.0 enables more free and flexible use and distribution, promoting open collaboration and innovation. It can be a good choice to make your models widely available and provide access which is reliable and high-quality. (https://www.apache.org/licenses/LICENSE-2.0)
If it looks good to you, you can choose to update other yi derivatives (if you have) license to apache-2.0 on your own if I miss out.
2. Recommendation for Yi Derivatives:
All Yi Series models are now licensed under apache-2.0. It is recomended that Yi derivatives mention the specific Yi models they're based on in any place (e.g., in the Model Card) to align with the requirement of apache-2.0.
Thanks for your continued support and contributions to Yi models.

README.md

@@ -1,7 +1,5 @@
 ---
-license: other
-license_name: yi-license
-license_link: LICENSE
+license: apache-2.0
 widget:
   - example_title: "Yi-34B-Chat"
     text: "hi"