Please add explaination to README how to run ZeroNet with tor

You should add a section: "Tor connectivity", and explain there that by default ZeroNet connects through the clearnet, and requires either UPnP feature on the router, or manually opened port #. In case of ```--tor=always```, on the other hand, open port isn't needed, but torrc should have ..... and explain what is actually required from Tor.

This pertains to basic connectivity, and should be in README, IMO.