Doc improvements/suggestions

[aperepel]

• On IP addresses - mention these are typically private network IPs for dual-homed nodes
• Explain the 2375 port (non-secure swarm), as docker machine creates TLS instances by default on 2376
• Explain/give examples for the node1, node2, ..., nodeN (basically highlight Consul IPs vs cluster nodes IPs)
• Document the add() command, it's already implemented ;)
• Mention that the host running the munchausen container becomes a swarm master node

[martonsereg]

Improved documentation in: https://github.com/sequenceiq/munchausen/pull/19