You can already do that using the built-in wikipedia feature; I'd rather have that one fleshed out a bit. I actually would be against this being the default thing when you right click an object, however an interesting idea would be to be able to set a description for an object so that if you created a simulation and you wanted to put some footnotes about your planets, when someone right-clicks it they can read the description you put in.
If that gets implemented I could see someone opening one of the default simulations and giving everything descriptions.