Reformat the help function in __main__.py

[NicolasCARPi]

Hello,

Pretty trivial change in the end, but I wanted to take a break from typescript/php, and because I want to familiarize myself with the codebase, my first entrypoint was __main__.py of course, and saw it could benefit from this small change.

Best, ~Nico

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• replace ... with [options] in doc comment
• move available_scripts variable in help_and_exit function scope
• use sorted instead of a two steps conversion/sort
• use formatted string

[FlorianRhiem]

Hey Nico, thank you for the pull request. I've changed the print slightly to be more readable and to preserve the order of messages more clearly.