Add some docs for the `:ns-list` option

I'm moving descriptions of options away from the Usage section, because
I don't want needless details to bog down your first impression of the
app - and especially not before you encounter the Debug section.
Rename :ns-list to :app-namespaces
Add @andrewmcveigh to list of Contributors
Add :url and :license to project.clj
Release 0.6.0