Update docker-compose documentation for service "configs"

[thaJeztah]

See docker/cli#83

/cc @cpuguy83 @shin- @londoncalling

[londoncalling]

@thaJeztah @shin- @dnephin I'll need help with this one.

[mdlinville]

I can take this.

[mdlinville]

Closed via #3494

[docker-robott]

Closed issues are locked after 30 days of inactivity.
This helps our team focus on active issues.

If you have found a problem that seems similar to this, please open a new issue.

/lifecycle locked