Option to add program description to the help text.

[dmitry-ryadnenko-izettle]

It would be nice to be able to add a more detailed program description to the help text. Like this.

Name: example
Description: runs example
Usage: example options_list
Arguments: 
    input -> Input file { String }
    output -> Output file name (optional) { String }

[codeape2]

Python's argparse (https://docs.python.org/3/library/argparse.html) has description and epilog, I suggest to implement something similar in kotlinx-cli as well.

parser = argparse.ArgumentParser(
    prog='ProgramName',
    description='What the program does',
    epilog='Text at the bottom of help'
)