Docker with Symfony and MongoDB

I want to make a project in PHP (Symfony) and MongoDB.

I created the file docker-compose.yml:

web_server:
build: .
ports:
    - 5000:5000
links:
    - mongo

mongo:
    image: mongo:3.0
    container_name: mongo
    command: mongod --smallfiles
    expose:
        - 27017

And I try to run Docker Compose in PHP Storm but I recived:

Removing old containers...
(Re)building services...
mongo uses an image, skipping
Building web_server
Cannot locate specified Dockerfile: Dockerfile
Starting...
Building web_server
Cannot locate specified Dockerfile: Dockerfile
No containers created for service: web_server
No containers created for service: mongo
Failed to deploy 'Compose:  docker-compose.yml': Some services/containers not started

I don't know what I should do, what should contain Dockerfile, what create containers.

Thanks!