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

[alexellis]

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 $ 

[AkihiroSuda]

You need 1.13 (RC): https://github.com/docker/docker/releases/tag/v1.13.0-rc3

[alexellis]

@AkihiroSuda yes, I'm aware, that's why I raised this issue - probably worth mentioning the 1.13 requirement on the README.md