Dockerfile to build docker container

[chriselsen]

Fixes #26 and provide as Dockerfile to build a local docker container.

First build the docker container.

git clone https://github.com/snstac/adsbcot.git
cd adsbcot/
docker build -t adsbcot .

Then run the docker container with the config folder mounted locally.
This way config files can be edited in the local folder /opt/docker/adsbcot/.

docker run -d -v /opt/docker/adsbcot/:/etc/adsbcot --name adsbcot adsbcot