CB-7345 improve cli documentation

This is odd -- it moves the description of what is required / optional down to the lower section, rather than showing it in the one-liner. I'd probably prefer something like

    cordova-cli build [PROD] [TARGET] [EXP] [PLATS] [-- [POPTS]]

    PROD:   --debug|--release
    ... etc

but that's a matter of preference. the bare "--", for instance, is really part of the overall command line, I think, not part of the platformopts, and it's almost hidden in the lower section.