Add a manpage

All the information in the manual page is copy pasted from Readme.
When any of the command line options are changed in the future, you can
update the info in the manpage and simply copy-paste it to the readme once
shown using man.
I've used simarrange as a command name, as it is easier to replace simarrange
wit sa, than to replace sa with simarrange.
sa is also used by psacct.