Document command line parameters

[lwcorp]

So far only their very usage was mentioned outside of the code only in #154, but TheForceEngine/main.cpp in void parseOption actually contains:

1. -gDARK or --game DARK: Directly load the Dark Forces game, skipping the titlescreen.
2. -r<replay_path>: Load a replay from the given path.
3. -nosound or --nosound:: Disable sound/audio.
4. -fullscreen or --fullscreen: Force fullscreen mode.
5. -skip_load_delay or --skip_load_delay: Skip loading delay (for faster startup).
6. --demo_logging: Enable Dark Forces demo logging (for dev/testing).
7. --exit_after_replay: Exit the program after a replay finishes.

Could you document them to https://theforceengine.github.io/Documentation.html?

And is it okay for me to add them to README.md?