Improve `--help` output to provide better messsages and usage of the library

[jorgecoca]

As stated in #5 , users might have trouble realizing what arguments they need to provide in order to use arb-converter.

[afpatmin]

In the meanwhile what is the proper command to convert json -> arb?

I've tried arb-converter to-arb --from-hierarchical-json .\en_GB\translations.json .\output.arb but no file is added (console output is empty)

[jorgecoca]

It'd be like this:

arb-converter to-arb ~/Downloads/ --from-hierarchical-json ~/Downloads/

This will get all the *.json files in Downloads, and convert them to arb inside Downloads

[felangel]

@jorgecoca I also made the same mistake as @afpatmin the first time I used the tool. I think it might be better to adjust the cli to align with expectations. Thoughts?

arb-converter to-arb --from-hierarchical-json ./path/to/input ./path/to/output

[jorgecoca]

Yep, I have nothing against that, especially if it is a pain point for many devs. Will try to work on this soon ;)