Tweak quickstart.md

[mcabbott]

• I think it's too obscure to say "cuDNN.jl has to be installed". We should just write the Pkg.add command out.
• The line model(noisy |> gpu) |> cpu is doing too many things, simplify?
• I don't like the "device = ..." pattern, but Carlo seems set on it, and added it here (instead of gpu). This at least tidies up a bit... most importantly never re-using x, y for things of different type.
• Maybe the name of that should be a verb not a noun? Like move = get_device()? Not done yet.

[CarloLucibello]

Maybe the name of that should be a verb not a noun? Like move = get_device()? Not done yet

I would stick to device, it is very familiar to pytorch users, and x |> device is nice, x |> move is not, although move(x) could be better than device(x) . to_device = get_device() could be another option, bu I still preferer device, also because get_device() returns an XDevice object.