Improve Dockerfile template

[jankeromnes]

Currently, the produced template seems to look like this:

MGlolenstine/open2internet@0b4365b

You'll notice that the apt-get install snippet is not on multiple lines like it should be.

Also, maybe we should suggest brew install instead, because it's much simpler to use (i.e. one single command to install, and the resulting version will not be an antique).