Created Cg shaders (markdown)

Cg-shaders.md

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+## Purpose
+Cg shaders is a spec from nVidia. It has the great advantage that shaders written in Cg are compatible with both OpenGL and Direct3D. It is also compatible with PlayStation 3 as well. They are also compatible with basic HLSL if some considerations are taken into account. They can even be automatically be compiled into [[GLSL shaders]], which makes Cg shaders a true "write once, run everywhere" shader format.
+
+### Example Cg shader
+    void main_vertex
+    (
+       float4 position : POSITION,
+       out float4 oPosition : POSITION,
+       uniform float4x4 modelViewProj,
+       float2 tex : TEXCOORD,
+       out float2 oTex : TEXCOORD
+    )
+    {
+       oPosition = mul(modelViewProj, position);
+       oTex = tex;
+    }
+
+    float4 main_fragment (float2 tex : TEXCOORD, uniform sampler2D s0 : TEXUNIT0) : COLOR
+    {
+       return tex2D(s0, tex);
+    }
+
+## Specification
+The Cg shader spec used in RetroArch is documented [here](https://github.com/Themaister/Emulator-Shader-Pack/blob/master/Cg/README). It defines single-pass Cg shaders as well as multi-pass shaders using a custom Cg preset format (.cgp).
+
+### Example Cg preset
+    shaders = 2
+    shader0 = 4xBR-v3.9.cg
+    scale_type0 = source
+    scale0 = 4.0
+    filter_linear0 = false
+    shader1 = dummy.cg
+    filter_linear1 = true
+