Update README.md

Author: lazuee

discord/channel-list-toggle/README.md

@@ -3,7 +3,9 @@
 > Displays a Menu icon only when it is not active, and reverts to its original state when it becomes active.
 
 ### Variables
-- `--channel-list-toggle-icon`: sets the default toggle icon of the channel list.
+- `--channel-list-toggle-icon-light`: sets the light mode toggle icon of the channel list.
+- `--channel-list-toggle-icon-dark`: sets the dark mode toggle icon of the channel list.
+- `--channel-list-toggle-icon`: sets the default toggle icon of the channel list without light/dark mode. (optional)
 - `--channel-list-toggle-icon-margin`: sets the toggle icon margin, if the icon size isn't 30x30.
 
 ### Preview