Update 2019-05-26: While having some familarity with roff is useful, since the time of originally have discovered Pandoc which can convert between many document formats, such as from markdown to roff. Writing documentation in markdown is just hard to beat. As the first text formatting program built for UNIX in 1970 running on a PDP-7, roff was a port of the BCPL program RUNOFF. Over the years roff has evolved into troff and the excellent GNU version groff.