cleanup llama-quantize --help output

[ddh0]

More pleasant formatting for the output of llama-quantize --help.

Before this PR:

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After this PR:

(this image was previously wrong, updated it to match the current code)

[compilade]

This is a very minor comment, which can be ignored if you want.

This kind of padding might cause unnecessary additional modifications when either adding a longer option (and args) than what exists currently, or when removing options or rewording args.
It's probably not really a problem, though.

But if we'd like to fix that anyway, how about having a constant for the padding (e.g. HELP_PAD or something), and using

    printf("%-*s%s\n", HELP_PAD, "--some-option and args", "some description");
    printf("%-*s%s\n", HELP_PAD, "", "rest of the description");

which is using the * syntax of fields in printf to get the padding from a variable. (And the - is for right-padding)

And then in the future, when padding is updated, we'll only need to change the value of the padding variable.

There could even be a macro for it (if desired):

#define HELP_PAD 42 // for example
#define PRINT_HELP(option, desc) printf("%-*s%s", HELP_PAD, (option), (desc))

Although if using macros, it's also possible to directly inscribe a compile-time known padding inside the printf call.

#define HELP_PAD "42" // notice it's a string
#define PRINT_HELP(option, desc) printf("%-" HELP_PAD "s%s", (option), (desc))

This uses the concatenation of adjacent literal strings in C, but then HELP_PAD (or equivalent) needs to be a literal string.

Keep in mind this is probably not necessary. Manual padding can work fine too. Like I said, feel absolutely free to ignore this suggestion.

Also note that the advantage of not padding is when using very narrow terminals (e.g. when using llama.cpp in Termux on Android). Padded line-wrapping can look weird (although it's already padded in the other examples which use the common/arg.cpp help printing)