Should mention minimum requirements.. unknown flag: --attachable

Would make sense to mention minimum requirements.

```
Node left the swarm.
pi@pi2swarm7:~/dev/spaceagency-funker $ docker network create --attachable -d overlay funker
unknown flag: --attachable
See 'docker network create --help'.
pi@pi2swarm7:~/dev/spaceagency-funker $ docker version
Client:
Version: 1.12.3
API version: 1.24
Go version: go1.6.3
Git commit: 6b644ec
Built: Wed Oct 26 19:06:36 2016
OS/Arch: linux/arm

Server:
Version: 1.12.3
API version: 1.24
Go version: go1.6.3
Git commit: 6b644ec
Built: Wed Oct 26 19:06:36 2016
OS/Arch: linux/arm
pi@pi2swarm7:~/dev/spaceagency-funker $
```

Locate the project’s Docker setup or usage documentation and compare its requirements with the Docker 1.12.3 client and server shown in the report. Document the minimum Docker version needed for `docker network create --attachable`, then verify the instructions against the relevant Docker command help.

Written by the indexing model from the issue text.