- document environment variables
- add missing --packages switch to command line
- describe how to pass template options to lxc-create (since
  lxc-create -h doesn't tell you)
- render help text in the same pretty format as lxc-create does
Signed-off-by: Tomáš Posíšek <tpo_deb@sourcepole.ch>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>