Add instructions to run uber-juno after installation

[ricguti]

I had some trouble waiting for Atom to setup Juno for me. After a while I figured out that I had to run uber-juno. I add the instructions necessary for this in setup.md.

[MikeInnes]

This won't be the right instruction for most people – you must have been re-installing juno rather than installing it for the first time?

[ricguti]

I was re-installing juno when this happened. I don't remember if this happen the first time I installed it. When I re-installed uber-juno all the packages that uber-juno installs were uninstalled, so I expected uber-juno to install them but that didn't happen until I ran uber-juno.

[Mari2061]

I had to install the uber.juno packege offline in atom. It loaded perfectly. But what to do next.. ( I´m totally new in atom and Julia)