Ignore docker compose override file

[chapa]

Summary

It would be nice to ignore docker-compose.override.y(a)ml so we can override the versioned docker-compose.yml without modifying it or being told by git that docker-compose.override.yml is an untracked file.

Use case

I use docker-compose.override.y(a)ml to add labels to the mattermost container in order to configure Traefik

Related resource

https://docs.docker.com/compose/extends/