Add a faq entry for "You should change path selection to avoid entering and exiting from the same country."

https://blog.torproject.org/blog/tor-browser-45-alpha-1-released#comment-79839 makes me realize that this is an ongoing question and I expect it will come up more with the new Torbutton interface for visualizing your paths.

What should users actually do with the information that, for example, their first hop and last hop are both in the US?

If we have an actual recommendation, we should change Tor to do that thing automatically.

I think the current situation is that there are many attacks and adversaries that Tor is trying to defend against at once, and constraining paths has surprising trickle-down effects on the other attacks (e.g. if I see where you exit then I know where you didn't enter, thus reducing your entropy, sometimes by a surprising amount depending on what path constraints we pick).

So the current advice amounts to "don't mess with it, you'll probably screw it up, we don't understand it very well either". We should figure out a way to concisely give people all the intuition that we have, so they can make good decisions.