Perhaps a Troubleshooting guide?
Also, a page listing different behaviour a Jira admin should expect to see with Jira Data Center. For example, you make a change in the admin screens in one node, how long might it take before you see the change when browsing another node? Just setting the expectation that changes take some time to propagate.
And perhaps note exactly what is run on each node and what operations are coordinated. For example, do all services run on all nodes, or are some restricted to just one node. Does the AD sync run on all nodes or just one?