Refs #1209 -- added a changelog entry for our license change

Also, from wiki: '''This version has been vetted
<https://en.wikipedia.org/wiki/Vetting> as an Open source license by the
OSI as "The BSD License".'''
On Fri Nov 07 2014 at 9:45:43 AM Paul Kehrer <notifications@github.com>
wrote:

> In CHANGELOG.rst:
>
> > @@ -6,6 +6,9 @@ Changelog
> >
> >  .. note:: This version is not yet released and is under active development.
> >
> > +* Cryptography has been relicensed from the Apache Software License, Version
> > +  2.0, to being available under *either* the Apache Software License, Version
> > +  2.0, or the BSD license.
>
> I suppose that should be sufficient as it's a reference to the actual
> license file that we explicitly include.
>
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> <https://github.com/pyca/cryptography/pull/1461/files#r20008193>.
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