Update "docker-compose up" doc to explain logging (#4672)
Update "docker-compose up" doc to explain logging (#4672)

After running "docker-compose up", the console shows a nice aggregated output of each container. When running this in detached mode, it's not clear how to later view this aggregated output again. Added a quick note on how this is done.
anweiss/docker.github.io,thaJeztah/docker.github.io,johnstep/docker.github.io,londoncalling/docker.github.io,anweiss/docker.github.io,docker/docker.github.io,anweiss/docker.github.io,docker/docker.github.io,JimGalasyn/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,londoncalling/docker.github.io,thaJeztah/docker.github.io,JimGalasyn/docker.github.io,londoncalling/docker.github.io,JimGalasyn/docker.github.io,anweiss/docker.github.io,JimGalasyn/docker.github.io,thaJeztah/docker.github.io,JimGalasyn/docker.github.io,johnstep/docker.github.io,johnstep/docker.github.io,docker/docker.github.io,docker/docker.github.io,londoncalling/docker.github.io,johnstep/docker.github.io,londoncalling/docker.github.io,johnstep/docker.github.io,anweiss/docker.github.io