added rainbow

doc/profile.conf.example

@@ -233,6 +233,10 @@ TERM=xterm-256color
 # Leave unset to keep the terminal-size-based dynamic default.
 #RAIN_DEFAULT_DENSITY=80
 
+# rainbow: Horizontal color shift speed — integer/100 gives seconds (4 → 0.04 s).
+# Values < 1 are used as raw seconds.
+#RAINBOW_DEFAULT_SPEED=4
+
 # matrix: Falling speed.
 #MATRIX_DEFAULT_SPEED=3.5