message: Update README.md
  Mention Metal support
diff: @@ -62,6 +62,7 @@ Here are a few sample materials rendered with Filament:
  - OpenGL 4.1+ for Linux, macOS and Windows
  - OpenGL ES 3.0+ for Android and iOS
  +- Metal for macOS and iOS
  - Vulkan 1.0 for Android, Linux, macOS and iOS (with MoltenVk), and Windows
  - WebGL 2.0 for all platforms
  @@ -90,7 +91,7 @@ Here are a few sample materials rendered with Filament:
  Many other features have been either prototyped or planned:
  -- IES light profiles
  +- IES light profiles/cookies
  - Area lights
  - Fog
  - Color grading
  