Documentation improvements for first timers

Hey,

Great work on the dev environment.

Comments while working through the setup:
- There is a delay from the time that `./bin/start` says the website is running until the time when it is actually running.
- This time is probably normal spin up time, but it might be worthwhile and preemptive to state that there might be some delay.
- Also noted that the setup container shuts itself down once the system is running. When looking at my docker widget I wasn't sure if this is normal, but the system appears to be running. If this is normal and expected it might be worth noting.

Now my question, If I were to be writing a rails ruby module, how should I be running the tests (e.g. ActiveTest)?
- Does the website have to be running at that moment? Or just parts of it (DB, etc).
- Are they run locally, or do you have to shell in to one of the docker containers?

I'm happy to PR the documentation with these updates

Thanks