Update README.md with license information

We (01.AI) have updated our license from yi-license to apache-2.0.
Since apache-2.0 enables more free and flexible use and distribution, promoting open collaboration and innovation, we kindly advise that all Yi derivatives currently under the yi-license be updated to the apache-2.0 license.
Thanks for your understanding and cooperation.

README.md

@@ -1,7 +1,5 @@
 ---
-license: other
-license_name: yi-license
-license_link: LICENSE
+license: apache-2.0
 ---