add "lxc --help" output to README

The "lxc --help" output can server as a reference to
the interested user on what lxctl provides as functionality
and als as a "web manpage".
Merge pull request #25 from tpo/master

Include --help output in README
Removed Makefile reference from README.
Fix : when CONF_DIR and roots fs are both on a lvm LV.