I had to set up a ZK ensemble the other day for the first time in a while, and thought I'd test our docs on the subject while I was at it. I headed over to https://lucene.apache.org/solr/guide/setting-up-an-external-zookeeper-ensemble.html, and...Well, I still haven't gotten back to what I was trying to do, but I rewrote the entire page.
The problem to me is that the page today is mostly a stripped down copy of the ZK Getting Started docs: walking through setting up a single ZK instance before introducing the idea of an ensemble and going back through the same configs again to update them for the ensemble.
IOW, despite the page being titled "setting up an ensemble", it's mostly about not setting up an ensemble. That's at the end of the page, which itself focuses a bit heavily on the use case of running an ensemble on a single server (so, if you're counting...that's 3 use cases we don't want people to use discussed in detail on a page that's supposedly about not doing any of those things).
So, I took all of it and restructured the whole thing to focus primarily on the use case we want people to use: running 3 ZK nodes on different machines. Running 3 on one machine is still there, but noted in passing with the appropriate caveats. I've also added information about choosing to use a chroot, which AFAICT was only covered in the section on Taking Solr to Production.