Compose file update and readme addition

Merged Nevin Morgan requested to merge vividfront/meltano/files-docker-compose:master into master

@DouweM First stab at a compose file for meltano and an accompanying readme. I am not using Airflow and I also don't have any experience with it, so if someone else could test the bit about it under "Adding services" to verify my instructions that would be great. I am also completely down with removing that section as well. Let me know if that helps and if there are any other service additions you would like me to add to the readme in the bundle, or anything else you think might be helpful.

Edited by Nevin Morgan