This is one of 4 multi-cluster topologies we will eventually document (multi-primary, primary-remote, external-control plane and federation) under the general topic of "multi-cluster".

Community sail-operator documentation: https://github.com/istio-ecosystem/sail-operator/blob/main/docs/README.md#primary-remote---multi-network (note the pre-reqs earlier in the doc).

Note that the above describes a "multi-network" setup, and there is also a (much simpler) single network setup documented upstream: https://istio.io/latest/docs/setup/install/multicluster/primary-remote/

Product documentation should cover both options.

Addition: Should also include instructions for configuring Kiali with this topology.