Mention dattorro reverb in man page

Author: derselbst

doc/fluidsynth.1

@@ -241,7 +241,7 @@ Choose interpolation method for one channel
 .B REVERB
 .TP
 .B set synth.reverb.active [0|1|2|3]
-Select reverb engine (0=off, 1=FDN, 2=freeverb, 3=LEXverb). Engine selection applies at synth creation.
+Select reverb engine (0=off, 1=FDN, 2=freeverb, 3=LEXverb, 4=Dattorro). Engine selection applies at synth creation.
 .TP
 .B set synth.reverb.room-size num
 Change reverb room size