Update documentation on ShaderToy uniforms

Clarify the explanation of ShaderToy uniforms and vertex shaders.

Author: Snorfield

docs/index.md

@@ -8,7 +8,7 @@ All shader code here is written to be valid **GLSL** or **OpenGL Shading Languag
 ## Variables
 
 ```js
-Shader Inputs
+// ShaderToy uniforms
 uniform vec3      iResolution;           // viewport resolution (in pixels)
 uniform float     iTime;                 // shader playback time (in seconds)
 uniform float     iTimeDelta;            // render time (in seconds)
@@ -23,6 +23,10 @@ uniform vec4      iDate;                 // (year, month, day, time in seconds)
 
 These are the uniforms defined by **ShaderToy**, and the shader examples in this library use them, as mentioned before, for ease of testing.
 
+If ShaderToy does not have a uniform for a certain thing that the shader requires, it will be explained in the article, and the uniforms will still follow the naming convention for ShaderToy. An example of this is **vertex shaders**. As ShaderToy is mainly a playground for **fragment shaders**, there's nothing like `uniform mat4 iModel;`. However, we still have a section for vertex shaders, they just won't be able to run in the ShaderToy environment.
+
+Articles will explain any uniforms not available in ShaderToy, and you can refer back here to get an explanation for any uniforms which are available in ShaderToy.
+
 Other shading langages, such as Godot's shader language, are quite similar to GLSL, and therefore easy to adapt these shaders to.
 
 ## Contributing