Please add license to repo.

[jmonroynieto]

Hello,

I noticed that this repo is missing a license while intending to put in a pull request because I found a couple of bugs. This indicates that the rights of the code are all reserved.

Having the code publicly available as indicated in the publication makes me think the intention for this source code is to be open source. Even if this is not the case, I think it would be best to understand what limitations we have when using this software.

Could the maintainers please add a license?

[LiTang1013]

您的邮件我已收到，谢谢！