Add a prompt on Slick Greeter when switching to Wayland Session

[nozomi-75]

I've encountered multiple instances already where people have attempted to switch to the Wayland session (in Cinnamon ofc) to check it out. Some cases however, they encounter a terrible issue or end up with an 'unusable' desktop. Though can be dealt with by switching back to X11, some struggle to deal with this situation.

Maybe a simple warning prompt before switching to Wayland session, while it is still experimental, would be helpful. What do you guys think?