Add note about element reference equality bailout in Optimizations, maybe Reconciliation?

[samsch]

Could the bailout described here be added to the React documentation in the Optimizations or reconciliation page (and maybe a note in the other)?

Currently this functionality seems to be undocumented, which means the React docs don't properly match the public API right now. The closest thing is the second paragraph Avoid Reconciliation here. This at best only might imply the functionality. Would be great to have it explicit.