Syntax: %bSET <channel> ENTRYMSG <message|->%b

Sets the entry message for <channel> to <message>.  When
users enter the channel, %C will send them the message.
To clear the entry message use a "-" as the message.
Alias: %bONJOIN%b
Examples:
         %b/msg %C SET <channel> ENTRYMSG Welcome!%b
           Sets the entry message to "Welcome" on <channel>

         %b/msg %C SET <channel> ENTRYMSG -%b
           Clears the entry message on <channel>
