should we add a paragraph that the proxy and the web application server may run on the same or different server(s)? and explain our terminology in the parameters: `server` is the dns name/ip and optional port of a caching proxy, while `host` is the domain name of your web application as used by the client.

we could also check in the code if we are consistent with this. i think we two understand what each is, but it can be confusing to beginners, and its crucial to always understand which of the two you are talking about when configuring and using the invalidator.