Change 'help help' text: 'help cb' to 'help bc'

Current text:

```
Command? help help

	Help for main menu commands, e.g. "help ver" for version number and logo, "help cb" for broadcast … etc.
	
	Note:
		Using "help" with no operand at the main menu simply redisplays the menu.
	Arguments:
		Command uses the choice variable, passed from the commandentry function.
	User input:
		User input is not intended within this function.
```