add
Directly register a ChatCommand to this command registry.
Generally speaking, you shouldn't call this directly - instead, create an Extension and call the ChatGroupCommand.chatCommand function in your Extension.setup function.
This function will throw a CommandRegistrationException if the command has already been registered, if a command with the same name exists, or if a command with one of the same aliases exists.
Parameters
command
The command to be registered.
Throws
Thrown if the command could not be registered.