Don't ask users whether to associate connections

[Malabarba]

We should just assume that the user is creating the connection from inside the project, and save a lot of people some confusion. And say on the command's docstring (and the readme instructions) that the command should be invoked from within the project.
And then have a custom option to not use that assumption

[bbatsov]

The new default is - if you're in a project, use it, if not - prompt for a project.

Btw, an even better solution would be to insert the project dir (if available) in the nREPL session description.