Heroku Postgres-SQL DB connection with binary buildpack

Im trying to host my server on Heroku with a Postgres-SQL database via the docker-compose yml example but im struggling to find any documentation on it. I’ve heard people mentioning the binary buildpack and got it to work but I’m not sure what to do next. I’ve also taken a look at the heroku article on container-registry-and-runtime but it doesn’t seem to have my specific use case. If someone has a quick copy paste or something they could whip out that would be best, but any guidance would be beneficial as well.