Running cfviz-frontend without arguments provides incorrect usage string

[Botond Ballo]

Here is the usage string I get when running cfviz-frontend without arguments:

USAGE: cfviz-frontend <INPUT> --annotate <ANNOTATE>

Here is the one I get when running cfviz-frontend --help:

USAGE: cfviz-frontend [FLAGS] [OPTIONS] <INPUT>

The two usage strings should be the same. It looks like the second is the correct one.

[Derek Berger]

switch to custom usage message when no arguments (fixes #28)

→ <<cset 020fca45d6c0>>