Added basic, untested Dockerfile

This will be the basis for the docker support. I haven't
gotten it working yet as I need to make some other changes to
the script. Should this be kept as a separate branch...?

Dockerfile

@@ -0,0 +1,10 @@
+FROM python:3.13.2-alpine3.21
+
+WORKDIR /usr/src/app
+
+COPY discorss.py ./
+COPY discorss.conf /etc/
+
+RUN pip install --no-cache-dir requests feedparser
+
+CMD [ "python", "discorss.py" ]