Update available shaders in README

Author: adamgraham

README.md

@@ -18,6 +18,8 @@ To load a package from a Git URL:
 
 ### Surface
 
+- Checkerboard
+- Cubemap
 - Decal
 - DetailTexture
 - Diffuse
@@ -26,18 +28,12 @@ To load a package from a Git URL:
 - Ramp
 - RimLighting
 - SingleColor
+- ShadowCasting
 - Sliced
 - SpecularSimple
 - WorldReflection
 - WrappedDiffuse
 
-### Lit
-
-- Diffuse
-- DiffuseSimple
-- DiffuseWithShadows
-- ShadowCasting
-
 ### Unlit
 
 - Checkerboard