message: Mention pbrt-parser in readme
diff: @@ -46,6 +46,7 @@ Additionally, in order to compile the viewer application and the [examples](http
  - [Libpng][8] (optional)
  - [LibTIFF][9] (optional)
  - [OpenEXR][10] (optional)
  +- [PBRT-Parser][11] (optional)
  @@ -149,3 +150,4 @@ Visionaray is licensed under the MIT License (MIT)
  [8]: http://libpng.sourceforge.net
  [9]: http://www.libtiff.org
  [10]: http://www.openexr.com/
  +[11]: https://github.com/ingowald/pbrt-parser
  