When giving a webtunnel bridge, we should explain that it's not using ipv6

We keep hearing from confused users who get a webtunnel bridge from bridges.torproject.org, and think they have been given an ipv6 one because the lines look like

webtunnel [2001:db8:5e01:4e45:956e:bdcd:b32:d2f1]:443 [...]

They especially think there is some bug because there is a "do you need ipv6?" button and they don't check it and boom they get an ipv6 bridge.

But! It's secretly not even an ipv6 bridge, this is a fake address that we put in the bridge line to help Tor know to expect different fingerprints for different bridges.

In an ideal world, we would change the design to stop using a big ipv6 address at the beginning, so users no longer get confused. But @shelikhoo rightly points out that the ipv6 address can fit a lot more bits so there is some value to keeping it.

So my backup idea is: let's include some words every time we give somebody a webtunnel bridge (over https, over email, etc) that explain that your Tor will connect to the address in the url argument and it will ignore the ipv6 address.