fix: update manpage

Author: Texarkanine

cmatrix.1

@@ -36,7 +36,7 @@ Locks cmatrix, Unable to quit
 Print usage and exit
 .TP
 .I "\-r"
-"Rainbow" mode, rainbow colored character
+"Rainbow" mode, rainbow colored characters. Uses colors from -C if multiple are specified, otherwise uses the full rainbow palette.
 .TP
 .I "\-k"
 Every characters change