[docker-compose] mention ipv6 for localhost problem

[arthurzenika]

Proposed change

Context

Your Environment

• FaaS-CLI version ( Full output from: faas-cli version ):

• Docker version docker version (e.g. Docker 17.0.05 ):

• Are you using Docker Swarm or Kubernetes (FaaS-netes)?

• Operating System and version (e.g. Linux, Windows, MacOS):

• Link to your project or a code example to reproduce issue:

• Please also follow the troubleshooting guide and paste in any other diagnostic information you have: