README - state that using lxc as the exec driver isn't the only way to gain shell access
README - state that using lxc as the exec driver isn't the only way to gain shell access

Because shell access can be gained by running an SSH server or
equivalent within the container.

Signed-off-by: Pang Yan Han <9d8a3bce71455786d192cd4b985538c54e03f109@viki.com>

viki-org/storm-docker,viki-org/storm-docker