Add a dockerfile

[MrARM]

Hey!
Here's a small change to add a Dockerfile to test locally in a clean and environment-agnostic manner.

To use, you just need to build and run it,
To build

docker build -t sondehub-tracker .

And, to run

docker run --rm -p 8000:8000 --name sondehub-tracker sondehub

If you'd like to run in the background and not terminate after you exit your terminal, replace --rm with -d.

[LukePrior]

Thanks, looks good.