Add LICENSE

[felipeqq2]

Hey! I noticed that this repository doesn't have any license information, either in the README or the appropriate LICENSE file. The package.json does mention ISC, but this is not available anywhere else.

https://github.com/raindropio/app/blob/ecee96e3f1b23b3c99dd71f66df8b3ab4f374539/package.json#L6

I believe that this project is open-source (as stated on its homepage), and properly licensing it is an important step to make it available to further development. You can check out Choose a License for more information on this.

Note that the same issue is also present in your other repositories, such as raindropio/mobile and raindropio/desktop.