message: Update README
  Better describe what the first document is about.
diff: @@ -11,9 +11,9 @@ Android devices and as the renderer inside the Android Studio plugin.
  ## Documentation
  -- [Filament](https://google.github.io/filament/Filament.md.html), an in-depth explanation of the graphics capabilities and
  - implementation of Filament. This document explains the math and reasoning behind most of our
  - decisions.
  +- [Filament](https://google.github.io/filament/Filament.md.html), an in-depth explanation of real-time physically
  + based rendering, the graphics capabilities and implementation of Filament. This document explains the math and
  + reasoning behind most of our decisions. This document is a good introduction to PBR for graphics programmers.
  - [Materials](https://google.github.io/filament//Materials.md.html), the full reference documentation for our material system.
  This document explains our different material models, how to use the material compiler `matc` and
  how to write custom materials.
  