avoid docker build again and again code example

Example 1: docker-compose update code without using build again

docker-compose up -d --build

Example 2: not reinstalling packages on docker build

FROM my/base

WORKDIR /srv
ADD ./requirements.txt /srv/requirements.txt
RUN pip install -r requirements.txt
ADD . /srv
RUN python setup.py install

ENTRYPOINT ["run_server"]