Add a license

[jzimmek]

reactively seems like a really nice and concise library.

do you intend this project being used by others? it would be great if you could add a LICENSE to the project.

if you intend this project more for experimentation / education only, just close this issue.

keep up the good work!

[Milo Mighdoll]

Thanks for the kind words! It would be awesome if others used and adapted this library!

I've also added a MIT license file to clarify licensing.