Add license information.

[fgregg]

Hi @slacy, would you mind clarifying the licensing for this project. I wrote a python wrapper for your code and I want to make sure that it's kosher. https://github.com/datamade/doublemetaphone

[sarimak]

When reading the README of this GitHub repo, the license of the double-metaphone library seems to be the same as Perl license -- thanks to "This module is free software; you may redistribute it and/or modify it under the same terms as Perl itself." quote from the original codebase. According to https://dev.perl.org/licenses/ Perl is dual-licensed: GPL 1+ or Artistic license.

Artistic license is available at https://dev.perl.org/licenses/artistic.html -- and according to https://choosealicense.com/licenses/artistic-2.0/ (which is referenced to from GitHub licensing HOWTO) it
allows re-distribution of the library even as a part of a commercial product under liberal conditions not too far from MIT or BSD licenses.

I would expect that the Python wrapper for this library could use the Artistic license as well.