readme: add explaination about the MC command prompt
readme: add explaination about the MC command prompt

fixes #22

Signed-off-by: Gaetan de Villele <9e9aedc08ce54c2f5baa13ea4ed4212fe28a9f42@gmail.com>

johnmccabe/dockercraft,docker/dockercraft,nyasukun/openstackcraft,docker/dockercraft,johnmccabe/dockercraft,gdevillele/dockercraft,gdevillele/dockercraft,gdevillele/dockercraft,nyasukun/openstackcraft,nyasukun/openstackcraft,johnmccabe/dockercraft