HourCycle docs are wrong

[hsivonen]

https://unicode-org.github.io/icu4x/rustdoc/icu/locale/preferences/extensions/unicode/keywords/enum.HourCycle.html says:

H11
Hour system using 1–12; corresponds to ‘h’ in patterns
H12
Hour system using 0–23; corresponds to ‘H’ in patterns
H23
Hour system using 0–11; corresponds to ‘K’ in patterns
H24
Hour system using 1–24; corresponds to ‘k’ in pattern

The doc for H24 is correct, but the other three have a mismatch between the doc and the enum value.

Additionally, the docs should try to make an effort to minimize misuse. Specifically, the docs should say:

H24 isn't used anywhere and is not what's usually understood as the "24-hour clock".
H11 is only used in Japan.
H23 is "24-hour clock".
H12 is "12-hour clock".