Add a LICENSE.txt

[Ryuno-Ki]

Hey there!

I just ran into your demo as I was looking for something helping me with a game jam.
Very nice work!

Could you add a LICENSE.txt file to highlight that your code is released under the MIT license (as stated in the README)?
https://choosealicense.com/licenses/mit/ has the license text.

It's one of the first things I look for when deciding on adopting a library.

Thanks for making it!