title: in docker python cannot find app
body: <p>When I run "<code>docker-compose up</code>" on Windows 10 docker client, I get the following errors:</p>
  
  <pre><code>counterapp_web_1 |   File "manage.py", line 7, in &lt;module&gt;
  counterapp_web_1 |     from app import app
  counterapp_db_1 | 2018-01-26T05:09:23.517693Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
  counterapp_web_1 | ImportError: No module named 'app', 
  </code></pre>
  
  <p>Here is my dockerfile:</p>
  
  <pre><code>FROM python:3.4.5-slim
  
  ## make a local directory
  RUN mkdir /counter_app
  ENV PATH=$PATH:/counter_app
  ENV PYTHONPATH /counter_app
  
  # set "counter_app" as the working directory from which CMD, RUN, ADD references
  WORKDIR /counter_app
  
  # now copy all the files in this directory to /counter_app
  ADD . .
  
  # pip install the local requirements.txt
  RUN pip install -r requirements.txt
  
  # Listen to port 5000 at runtime
  EXPOSE 5000
  
  # Define our command to be run when launching the container
  CMD ["python", "manage.py", "runserver"]
  </code></pre>
  
  <p>There is a <code>manage.py</code> to call folder <code>app</code>, under <code>app</code>, there is <code>__init__.py</code>.</p>