Correct organ.dsp example and documentation.

Faust.md

@@ -29,6 +29,8 @@ Other metadata:
 
 The [rack.lib](https://github.com/VCVRack/VCV-Prototype/blob/faust/res/faust/rack.lib) Faust library contains usefull functions to convert CV signals, and can be enriched if needed. 
 
+Note that **only monophonic DSP programs** can be described. 
+
 ## DSP examples
 
 Here is a simple example showing how oscillators can be controlled by GUI items, associated with metadata in the DSP code:

examples/organ.dsp

@@ -1,7 +1,7 @@
 import("stdfaust.lib");
 import("rack.lib");
 
-vol = hslider("vol [knob:1]", 0.3, 0, 10, 0.01);	
+vol = hslider("vol [knob:1]", 0.3, -70, 5, 0.01) : ba.db2linear;	
 pan = hslider("pan [knob:2]", 0.5, 0, 1, 0.01);	
 
 attack = hslider("attack", 0.01, 0, 1, 0.001);