Clarify software license

[apeterson91]

In your DESCRIPTION file, you list the license as GPL-3, while in the header for file R/RNG.R
the license text states

...
you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

suggesting that the code is covered under GPL-2.

Could you please clarify which license your software is formally covered under? Adding a specific LICENSE file to your repo would also help in this matter.

[renozao]

@apeterson91 I updated License information across the package.
Please let me know if I missed something.
Thanks