Polly subproject release notes

[Hans Wennborg via llvm-commits]

On Wed, Aug 26, 2015 at 3:24 AM, Tobias Grosser via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Hi Hans,
>
> if still possible last minute, I would like to contribute the release notes
> for the Polly subproject.

Thanks! r246053.