Document way of forcing a re-render

Thanks for devcards! It's been very helpful in demoing the power of ClojureScript :)

I'm using Shadow-CLJS, and I couldn't find a way to force dev-cards to be re-rendered upon a hot-code reload event. I see my code been reloaded, but calling `(dc/start-devcard-ui!)` doesn't update the interface.

I've found the workaround of calling `(devcards.system/renderer @devcards.system/app-state)` after the hot-code reload and this seems to do the trick. I wonder if this should be documented or be made official, as I'm not sure if this is supposed to be public API or not.

Thanks again, and happy new year!

Start by reviewing the reported Shadow-CLJS hot-code reload behavior, including dc/start-devcard-ui! and devcards.system/renderer with @devcards.system/app-state. Determine whether the renderer call is supported, then document the confirmed way to force a re-render or clarify that the behavior is not public API.

Written by the indexing model from the issue text.