Add a section on how user can run CDK and upstream Minishift in parallel

Red Hat CDK and Upstream Minishift both uses ~/.minishift as the home directory. By default, Minishift/CDK place all runtime state into ~/.minishift. So users can not run both in parallel without separating the home directories for CDK and upstream Minishift.

To separate the home sirectory can use the MINISHIFT_HOME environment variable, to choose a different home directory for Minishift.

Original issue https://issues.jboss.org/browse/CDK-210