Improve typing of `help()`

[KSXGitHub]

Currently, help functions accept any array of strings. It would be nice if help parameter can be narrowed down to specific union of string tuples.

For example: Let's say our application supports a main command and 3 subcommands which are foo, bar, and bar baz, then type of cmdPath parameter of help of main command should be [] | ['foo'] | ['bar'] | ['bar', 'baz']