Adding example about how to disabling automatic unmounting component

Adding an example for who don't want components being unmounted.
I'm not a huge fan of this hack as a whole but while it exists let's make the example even clearer. Can we call it `MyRootComponent` or something similar so it's clear that this doesn't work for components at arbitrary depth. There's a danger there as in theory a component shouldn't know if it's the top-most since you could render the same component as a child elsewhere. But I suppose that's probably not what most people are doing so let's just make it as clear as possible.