Add an Options and Menu

so a user can do the following:

```text
$ perl ~/GitHub/perl-prereqscanner/bin/scan_prereqs --help
Usage:
        scan_prereqs [--combine] [DIRS|FILES]

    Directories are traversed with File::Find to collect all ".pl", ".pm",
    ".psgi" and ".t" files. If no directories or files are specified, the
    current working directory is scanned.

```