Automate image build for docker-compose

[bbworld1]

The px4flightreview image does not exist until you build it manually, meaning the docker-compose config will not launch until you build the Dockerfile. Combined with a relative lack of documentation, this leads to user confusion.

It would be best to add a build: section in the docker-compose configuration, which will automatically build and tag the image when the configuration is run.

Side note: have we considered pushing an actual official px4flightreview image to Docker Hub? It may be useful to have.

[bkueng]

Hi Feel free to suggest any changes you'd like to see via PR. Personally I don't use docker for this.

[bbworld1]

Thanks, I've added it at #207 here.

Docker Hub pushes are trivial to automate now that docker-compose handles building (simply docker-compose build, then docker-compose push), if that's an option you want to explore.