Added fader frag shader

assets/shaders/fader.frag.glsl

@@ -0,0 +1,10 @@
+#version 330 core
+
+in vec4 fColour;
+out vec4 colour;
+
+uniform float u_alpha;
+
+void main() {
+  colour = vec4(fColour.xyz, 1.0 - u_alpha);
+}