Commenting slope in materialInput

Source/Shaders/Builtin/Structs/materialInput.glsl

@@ -11,7 +11,7 @@
  * @property {mat3} tangentToEyeMatrix Matrix for converting a tangent space normal to eye space.
  * @property {vec3} positionToEyeEC Vector from the fragment to the eye in eye coordinates.  The magnitude is the distance in meters from the fragment to the eye.
  * @property {float} height The height of the terrain in meters above or below the WGS84 ellipsoid.  Only available for globe materials.
- * @property {float} slope The slope of the terrain normalized from 0 to 1.  Only available for globe materials.
+ * @property {float} slope The slope of the terrain normalized from 0 to 1.  0 is completely vertical, 1 is completely flat.  Only available for globe materials.
  */
 struct czm_materialInput
 {