Add license

[lnjX]

I (and probably also other people, as here: http://feathub.com/brexis/qml-bootstrap/+1) would like to use your work in our projects, but we can't use code without a license. So it would be great if you could add one (GPLv3-compatible would be nice).

<advertisment> Kaidan - https://github.com/kaidanim/kaidan </advertisment>