Could you add LICENSE file?

[hnakamur]

First of all, thanks for a nice software!

Could you add LICENSE file?
These pages might help for choosing a license.

• Open source licensing · GitHub Help
• Githubによる、オープンソースライセンスの選び方 | オープンソース・ライセンスの談話室

[kyokomi]

@hnakamur Thanks!

added the LICENSE file.

[hnakamur]

Thanks!