We asked a new person to follow the guide to start the docker using the image from docker hub yesterday, and it seems the word "replace" makes it confusing if the user is not cloning the EOSIO/eos github repo and just want to start the docker container immediately.

Just added a bit more clarity, because it's easy to miss that memory setting as written if you are unfamiliar with Docker and just assume that because you have a lot of memory your fine.

if we run original command, it makes error below
ERROR: .FileNotFoundError: [Errno 2] No such file or directory: './docker-compose-dawn3.0.yml'

After I changed .yml to .yaml, it works 
I think this maybe typo.

Thanks

(cherry picked from commit 80a8d3a9)

updated examples heading

Added compiling with eoscpp

added troubleshooting step to Docker readme

removed compiling step for now

Eventually I'd like proper Docker infrastructure, but this is a good
enough starting point just to demonstrate a proper development environment