After going through the docs to build the code outside the container myself, I update some of the instructions that were outdated.

Most importantly, we must be able to hit S3 from outside the container, thus we need to publish the S3 ports in docker-compose.yml.

If this is not worth doing only for out-of-container builds (as they are not recommended) I can amend the docs indicating the changes that need to be done to the compose file, and maybe add a sed onliner.