add pitchscaler cmd

doc/README.md

@@ -83,6 +83,12 @@ Parameters:
  - `law_freq`: LFO frequency (Hz), 2..30, default 9
  - `attendb`: Output attenuation (dB), -20..0, default 0
 
+## `pitchscaler split index mult`
+
+Runs the Higher Quality Pitch Scaler from the SWH plugins.
+
+The `mult` parameter is the pitch coefficient, range from 0.5..2, default 1.
+
 ## TODO `echo split index delay`
 
 Run an echo filter on the given loaded file.