Update raymarching.fs

Remove `fragColor` as it is unused

Move the license to the top of the code to improve readability.

examples/shaders/resources/shaders/glsl120/raymarching.fs

@@ -1,8 +1,32 @@
+// The MIT License
+// Copyright © 2013 Inigo Quilez
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// A list of useful distance function to simple primitives, and an example on how to
+// do some interesting boolean operations, repetition and displacement.
+//
+// More info here: http://www.iquilezles.org/www/articles/distfunctions/distfunctions.htm
+
 #version 120
 
 // Input vertex attributes (from vertex shader)
 varying vec2 fragTexCoord;
-varying vec4 fragColor;
 
 uniform vec3 viewEye;
 uniform vec3 viewCenter;