Feat: add Dockerfile and instructions on using Docker

[zealot128]

Added a Dockerfile + instructions, because I don't have any Python setup and always struggle with versions, Python version, Setup/Pyenv etc.pp.

This way, it makes it self contained and very simple and reproducible to run, especially if I already use Docker to run many software from the Internet :)

If you don't want to merge it, that's fine, too! Maybe other Docker users can find this PR then.

Thanks for the work, otherwise I might have killed a couple of weeks making my own in Rails ;)

[martin-ueding]

Docker is a nice idea. I've smoothed out some of the things in the documentation.

One issue likely is write access to the files outside, I think there needs to be done something. Or you create all these files as root?

[zealot128]

Yes you are right, it might be better to add a USER app or similar to the Dockerfile.

In my case it was not needed, as the Macos Docker runner runs as the user, so the data/* files are owned by my running user.

But this seems to do the trick:

 RUN mkdir /data

+ARG UID=1000
+
+RUN useradd -m -u $UID -d /app app && \
+    chown -R app:app /app && \
+    chown -R app:app /data
+
+USER $UID
+
 EXPOSE 5000

and than building with:

docker build --build-arg UID=`id -u`  -t geo-activity-playground  .

That way, the app-user matches the user that should run the docker container.