Update README.md

Author: xiaofan-luan

README.md

@@ -50,3 +50,8 @@ When we implement a new feature with new API, the following steps are recommende
 3. sync the modification to the milvus-proto, submit a commit
 4. in SDK project, sync the milvus-proto submodule to the commit and submit a commit
 5. develop SDK and main project parallelly
+
+## License
+Milvus proto repo is part of LF AI & Data Milvus project under Apache License 2.0.
+
+