--help with copy-ready examples; README uses commands instead of a flag table - #4

…ag table

--help (also -h, help) now prints to stdout: what fogping does, where data goes,
runnable examples for every common case (first try, login, several users,
--edit workflow, --days, background run/stop, --localhost, upgrade), the ICMP
permission fixes, and a short flag list. Every command in it was executed as
printed. Previously it was the flag package's dump on stderr, which did not
mention user=/passwd= at all.

A bad flag or bad user=/passwd= now prints one line and "Run './fogping
--help' for examples" instead of the whole usage; the --edit refusal shows a
working example.

README: the argument table is replaced by a "Common commands" section that
mirrors --help; the target form table is replaced by example targets.