Add doc for addressable terminators

[gberl002]

We should have documentation explaining what addressable terminators are.

Possibly reference some examples that use them (like the go SDK zcat example, as well as any others)?

Here is some existing documentation in a project wiki https://github.com/openziti/fabric/wiki/Addressable-Terminators

Also, there is a reference to the project wiki in the go sdk README for the zcat example. When the new doc is added to the doc site, the link in the example README should be updated to point to the official site doc.