We do not have any documentation for installing the OSSMC in the OSSM 3 docs. 

It is part of the OSSM 2 docs here: https://docs.openshift.com/container-platform/4.17/service_mesh/v2x/ossm-kiali-ossmc-plugin.html

Note: We should use a version compatibility table between OCP / OSSM / Kiali rather than mentioning individual versions in the doc, as we will have to maintain this going forward with each new Kiali release.

There is a related epic here for any engineering work needed to be done for OSSMC in 3.0: https://issues.redhat.com/browse/OSSM-6970