Add dockerfile and instructions in README

Dockerfile

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+FROM python:3.9-slim as base
+
+# The following is adapted from:
+# https://sourcery.ai/blog/python-docker/
+
+# Setup env
+ENV LANG C.UTF-8
+ENV LC_ALL C.UTF-8
+ENV PYTHONDONTWRITEBYTECODE 1
+ENV PYTHONFAULTHANDLER 1
+
+FROM base AS python-deps
+
+# Install pipenv and compilation dependencies
+RUN pip install pipenv
+RUN apt-get update && apt-get install -y --no-install-recommends gcc
+
+# Install python dependencies in /.venv
+COPY Pipfile .
+COPY Pipfile.lock .
+RUN PIPENV_VENV_IN_PROJECT=1 pipenv install --deploy
+
+FROM base AS runtime
+
+# Copy virtualenv from python-deps stage
+COPY --from=python-deps /.venv /.venv
+ENV PATH="/.venv/bin:$PATH"
+
+# Create and switch to a new user
+RUN useradd --create-home appuser
+WORKDIR /home/appuser
+USER appuser
+
+# Install application into container
+COPY . .
+
+# Run the application
+ENTRYPOINT ["python3", "-u", "main.py"]