Go to the tab General => Navigation, drag the green square on the right with Custom Route next to it over to the navbar looking area near the top. Then click the new Icon that appears and fill out the fields, put the url in the route field. Then click Enable and then click the Save Icon at the bottom right.
I suspect there will be a lot of customized stuff that we end up with when we actually do the import (though to be fair, while I think NodeBB is our leading candidate, it's not a done deal yet). We did a partial import from CS to Discourse, so a lot of the user deconfliction has already been worked through.
Most of what we do seems to be non-traditional.