Add CONTRIBUTORS or update README.

[zeekay]

@benoitbryon Any preference?

[benoitbryon]

In projects I maintain, I like CONTRIBUTORS (or AUTHORS) file. I use it to mention lead developer / maintainer (and optionnally original author if he is not the maintainer), then add a link to Github's contributors page. Some examples:

• https://github.com/diecutter/piecutter/blob/master/AUTHORS
• https://github.com/novapost/django-ticketoffice/blob/master/AUTHORS
• https://github.com/benoitbryon/django-downloadview/blob/master/AUTHORS

[zeekay]

Thanks, added in AUTHORS, and referenced you as a contributor. Hope that's okay :)

[benoitbryon]

Thanks!