add helptext for option -f (foreground)

[milahu]

currently the -f flag is undocumented

also the --debug flag is undocumented

[fangfufu]

Hmm, this is no longer working https://github.com/fangfufu/httpdirfs/blob/master/src/main.c#L242

[milahu]

just add the helptext to static void print_long_help(void)?

    -V  --version           Print version\n\
    -f                      Run in foreground\n\
        --debug             Print debug messages\n\

https://github.com/fangfufu/httpdirfs/blob/2fde39982ee4c41b6469b74237686e4b1837411d/src/main.c#L240-L246

add_arg(fuse_argv, fuse_argc, "-ho"); is a noop it just adds "-ho" to fuse_argv, but then what should happen?

[fangfufu]

add_arg(fuse_argv, fuse_argc, "-ho"); is a noop it just adds "-ho" to fuse_argv, but then what should happen?

FUSE should have printed out its own help messages. It used to happen.