diff --git a/README b/README
index 0f37449..b316d0e 100644
--- a/README
+++ b/README
@@ -10,3 +10,10 @@ double precision shaders.
 To build and run:
 
    ./build.sh && ./gpu-frac
+
+Since both GLSL and C use CPP directives, I parameterised the program
+a bunch and stuck a load of cool presets in config.h, which can be
+simply be uncommented and commented as is required.  All the #ifdefs
+make the code a bit harder to read but it's nice being able to twiddle
+numbers and change the visualisation without messing around editing
+and commenting out code.