Add MIT License to repo.

[Wulf]

Hi Hernán,

Thanks for this nice select plugin! Your comment from #37 said it's licensed under the MIT license, but I didn't find one in the repo.

Changes

• Added MIT license (LICENSE.txt)

Related to #43.

[craigdanj]

Please merge.. An MIT license would help integrating into other projects.

[doanguyen]

@hernansartorio another ping, please consider to add license file to the project. I also want to add this feature into my project.