Migrate from txt to md
Migrate from txt to md

Port the CentOS installation notes text to a prettier markdown
format. With the benefit of consolidating instructions in one place.

MarshallBrinn/geni-ch,MarshallBrinn/geni-ch,tcmitchell/geni-ch,tcmitchell/geni-ch,ahelsing/geni-ch,ahelsing/geni-ch