notes.txt: Update

doc/notes.txt

 + As threshold increases overall volume decreases - add a compensation algorithm.
 + THere are unintialized variable warnings on the release build.
 
+// May 22
++ Add invert to scale range to cause output to go in opposite direction.
+
+
 BUGS:
 // Apr 20
 The tempo measurement can produce invalid values.  Set score to 22 then play Mark 38.
 First tempo measurement is a non-sense value - probably produced by an div by zero.
+Also: Mark 8, Meas 10.
 
 Crash on playing Mark 37.