Add documentation or example for combo-box

[Tombert]

Howdy, I was trying to use the ui/combo-box macro, and I had a hell of a time since there was no documentation. I was able to figure out how to add list items by adding the :items ["my item"] thing, but I believe that that is something that should be documented, or at the very least, given an example.

I would be happy to help contribute to documentation if it would be useful.

[pmonks]

@Tombert a contribution of documentation would be fantastic! What kind of documentation system are you thinking of using (readme, GitHub wiki, inline docstrings, etc. etc.)?