Add description of STDIN mode to help command

[ydah]

❯ exe/lrama --help                                     
Lrama is LALR (1) parser generator written by Ruby.

Usage: lrama [options] FILE

+STDIN mode:
+lrama [options] - FILE               read grammar from STDIN

Tuning the Parser:
    -S, --skeleton=FILE              specify the skeleton to use
    -t                               reserved, do nothing

Output:
    -h, --header=[FILE]              also produce a header file named FILE
    -d                               also produce a header file
    -r, --report=THINGS              also produce details on the automaton
        --report-file=FILE           also produce details on the automaton output to a file named FILE
    -o, --output=FILE                leave output to FILE
        --trace=THINGS               also output trace logs at runtime
    -v                               reserved, do nothing

Error Recovery:
    -e                               enable error recovery

Other options:
    -V, --version                    output version information and exit
        --help                       display this help and exit