message: Mention Ptex
diff: @@ -47,6 +47,7 @@ Additionally, in order to compile the viewer application and the [examples](http
  - [LibTIFF][9] (optional)
  - [OpenEXR][10] (optional)
  - [PBRT-Parser][11] (optional)
  +- [Ptex][13] (optional)
  @@ -152,3 +153,4 @@ Visionaray is licensed under the MIT License (MIT)
  [10]: http://www.openexr.com/
  [11]: https://github.com/ingowald/pbrt-parser
  [12]: https://www.opengl.org
  +[13]: https://github.com/wdas/ptex
  