Manual clarification

[Taika-Kim]

Hi, I suggest a few manual clarifications for the wavetable editor:

Now it took me a while to realize, that there are both absolute and relative values and that they are set by the same parameter, only the "+" prefix tells the difference.

Also, it took me some time to realize, that all wavetables share the same 128 step area, altough this was basically mentioned in the manual...