Feature request: allow appending additional sections to output

[cxj]

I can obviously extend class Help and override method getHelp() to create a class of my own which does the following, but would you consider incorporating it into Aura.Cli itself? If so, I'll provide a PR.

I'd like to be able to append additional "sections" of output to what's returned by getHelp(), so that they would appear after the OPTIONS section. For example (via some quick hacking), an EXAMPLES section:

OPTIONS
    -v
    --verbose
        Verbose output.

    -h
    --help
        This help.

    -c [<value>]
        Config file directory (default: ./conf).

EXAMPLES
    generate build -v