Update key.md

Author: DSmolken

docs/opcodes/key.md

@@ -49,9 +49,9 @@ the lokey value it would set will override the previous lokey.
 lokey=70 key=72
 ```
 
-For cases where a region should not actually be triggered by a key (usually this
-is the case with regions triggered by MIDI CC changes), the special value of key=-1
-can be used.
+For cases where a region should not actually be triggered by a MIDI note message (usually
+this means a region triggered by MIDI CC changes, for example the movement of piano
+pedals), the special value of -1 can be used:
 
 ```sfz
 key=-1