Docker image not working

I am trying to install the lemmy to my vps using the docker approach following the guide in https://join-lemmy.org/docs/en/administration/install_docker.html . First, it gives a version error so I changed the topmost line to version: "3.5. But then I get the following error during sudo docker-compose up -d:

Building lemmy
ERROR: Cannot locate specified Dockerfile: docker/Dockerfile

I am not sure where is the mentioned dockerfile. So any ideas on how to proceed?