doc: add missing dep on curl

rpm calls rpm to retrieve to grab rpm over HTTP. That's something
we do to bootstrap the base install.
doc: add dep on libfrontier-rpc-perl

libfrontier-rpc-perl is a dependency of build/remove_system_on_rhn
script.
doc: yum-utils is required for yum-config-manager
Merge pull request #56 from enovance/bug/doc/goneri

doc: add missing dep on curl