Added Dockerfile

Dockerfile

+FROM python:3.7-alpine
+
+RUN pip install pipenv
+COPY . /opt/SpotifyBackup
+
+WORKDIR /opt/SpotifyBackup
+RUN pipenv install
+RUN ln -s $(pipenv --venv) /opt/SpotifyBackup/mypipenv
+
+CMD [ "/opt/SpotifyBackup/mypipenv/bin/python", "/opt/SpotifyBackup/SpotifyBackup.py" ]
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