Automating docker-compose with Github

I have recently set up an automated build repository by connecting my docker account with GitHub. I have made some small examples with a single Dockerfile in the project.

I have just a simple HTML file where I just print a paragraph, running it on NGINX. The Dockerfile looks as below:

FROM nginx:latest

LABEL   maintainer="JohnDoe" \

        name="DemoWebGit" \

        version="1.0"

ENV CONTAINER_HOME=/usr/share/nginx/html

WORKDIR $CONTAINER_HOME

ADD /myweb $CONTAINER_HOME

This works as I expected. Every time I push some code, the latest docker image is also built. If I have a release with a specific version, it works with the specific tag as I have configured it.

Now, I am trying to build a Flask based app which runs with gunicorn and NGINX. The NGINX flask depends on my Flask application. Thus, I had to fix this through the docker-compose feature. The docker-compose file looks as below:

services:
  nginx:
    image: nginx:latest
    container_name: nginx
    volumes:
      - ./default.conf:/etc/nginx/conf.d/default.conf
    ports: 
      - 80:80
    networks:
      - mynetwork
    depends_on:
      - myflaskapp
  myflaskapp:
    build: ./dockerfiles/Dockerfile
    container_name: myflaskapp
    command: gunicorn --bind 0.0.0.0:8000 "myflaskapp:get_app()"
    ports: 
      - 8000:80
    volumes:
      - ./:/var/www
    networks:
      mynetwork:
        aliases:
            - myflask-app

networks:
  mynetwork:

When I run docker-compose up this works just fine. However, I am trying to automate this one, but it seems that it always looks for the Dockerfile within the project. Now that I have two containers running simultaneously, I do now know how this can build a single image? Is there any way to automate this process and similar to this one, i.e. Php and MySQL?