add gate cmd

doc/README.md

@@ -178,3 +178,12 @@ with a suffix on the filename (before extension).
 
 Doing consecutive `quicksave`s will not overwrite any files, the suffixes will
 just be different.
+
+## `gate split index switch threshold attack hold decay gaterange` 
+
+ - switch (bool): 0..1, default 0
+ - threshold (dB): -70..12, default -70
+ - attack (ms): 0.1..500, default 30
+ - hold (ms): 5..3000, default 500
+ - decay (ms): 5..4000, default 1000
+ - gaterange (dB): -90..-20, default -90