setup: renamed shader files for automatic syntax highlighting

main.cpp

@@ -4,11 +4,11 @@
 #include <cstdio>
 
 const char *vertexShaderSource =
-#include "fsq.vs"
+#include "fsq.glsl"
     ;
 
 const char *fragmentShaderSource =
-#include "sdf.fs"
+#include "sdf.glsl"
     ;
 
 /*void framebuffer_size_callback(GLFWwindow* window, int width, int height)