Fix documentation for Command::after_long_help()

[pgerber]

Playground link showing that .afer_long_help() isn't shown with -h.

[epage]

As the documentation and the implementation diverge, an important thing to do is to determine which is "correct". I would generally recommend starting with an issue first, rather than a PR. However, I'm going to try to do that analysis here.

Current behavior

location	short	long	notes
before help	before_help	before_long_help or before_help	added in #2008, changed in #2174
command about	about	long_about or about	changed in #1612
arg help	help or long_help	long_help or help
subcommand about	about or long_about	about or long_about	changed in #2558
after help	after_help	after_long_help or after_help	added in #2008, changed in #2174

Docs mismatch

• before_long_help
• long_about
• after_long_help

The inconsistency in "command about"'s short and "subcommand about" is suspicious

Overall, this seems intentional enough with docs having been missed or changed as a result of a misunderstanding. I'm willing to go forward with this

[epage]

Thanks!