message: add news item to website
diff: News, Updates, and Announcements
  ================================
  +Sept 13, 2018: Version v1.7.0 now released on GitHub
  +---------------------------------------------------
  +
  +New release version 1.7.0 is now available on the [OSPRay GitHub
  +page](https://github.com/ospray/OSPRay/releases/v1.7.0).
  +
  +
  Jun 8, 2018: Version v1.6.1 now released on GitHub
  ---------------------------------------------------
  