Updated Add own functionality (markdown)

Add-own-functionality.md

@@ -63,4 +63,13 @@ Keep in mind that this will not cause interface updates as of 0.8.6. For that, y
 
 ### Create custom effects
 
-TBD
+It is possible to create your own effects and add them to the FX library.
+The relevant files for that are `FX.cpp` and `FX.h`.
+
+Here is a step-by-step guide on how to make your effect:
+
+1. Take a look at some of the effects in `FX.cpp` to see how they are implemented!
+
+2. TBD
+
+If you programmed a nice effect you want to share, submit a pull request!