[Enhancement] - add help argument

[JonShort]

Most CLI tools have a "help mode" which prints out the available args / commands

Something like this should exist for bumpall

E.g. bumpall help

...all available args printed with information

We do need to decide whether to have this as a flag (--help | -h) or an argument (see e.g. above)

Flag is consistent and probably easier to implement so that might be the best first step

[jaysc]

i think at this point we should just switch to a package.

This is the one I used before: https://docs.rs/clap/latest/clap/

[JonShort]

Agree - probably worth it now there's so many flags