Add very basic docker build

Dockerfile

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+FROM python:3
+WORKDIR /usr/src/app
+
+COPY requirements.txt ./
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+CMD [ "python", "./scan-feeds.py" ]

requirements.txt

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+pyyaml
+feedparser
+python-dateutil