Updated README to reduce duplication. #432

I feel like we need to define what actually belongs in docs and what belongs in the README.

IMO Docs are something the user would use to learn to _**run**_ Marathon while the README is something the user would use to learn to _**develop**_ Marathon.

As such, i feel like we should move all production/deployment related items into doc pages and update the README to be only about how to develop Marathon.