User's Guide: Runtime control: recommend the `+RTS --help`

In fish shell the +RTS -? simply does not work:

cabal v2-run hnix -- +RTS -?

fish: No matches for wildcard “-?”. See `help expand`.
command cabal v2-run hnix -- +RTS -?

Use of the -? is rather not very traditional, todays *NIX, GNU, POSIX tools mostly provide --help or -h - those two option uses are put in the specs.

Indeed, -? can be expanded by the shell as a pattern match symbol.

In case of fish shell - it tries to expand -? right there where it was put.

Let's recommend --help, because the -? behavior in different shells and uses of commands are unknown, idk how other shells would treat what universally is also a pattern match symbol. And because of the existence of the standard --help. Upon reading the help/using it more - users can themself switch to -? shorthand if it works for them.