document cli arguments

either I am blind or we dont have stuff for these:
https://github.com/PaperMC/Paper/blob/main/paper-server/src/main/java/org/bukkit/craftbukkit/Main.java#L48
should prolly go into the reference category next to the system props and stuff? 
easiest way prolly is to just print the joptsimple help and make it pretty