mention crackle in the documentation

src/documentation/learning/audio_engine/synths.ts

@@ -25,11 +25,13 @@ Note that you can also use noise if you do not want to use a periodic oscillator
 ${makeExample(
     "Listening to the different types of noise",
     `
-beat(.5) && snd(['brown', 'pink', 'white'].beat()).adsr(0,.1,0,0).out()
+beat(.5) && snd(['brown', 'pink', 'white', 'crackle'].beat()).adsr(0,.1,0,0).out()
 `,
     true,
   )}
 
+The <ic>crackle</ic> type can be controlled using the <ic>density</ic> parameter.
+
 Two functions are primarily used to control the frequency of the synthesizer:
 - <ic>freq(hz: number)</ic>: sets the frequency of the oscillator.
 - <ic>note(note: number|string)</ic>: sets the MIDI note of the oscillator (MIDI note converted to hertz).