Hello :)
This is a great feature request, I've added that to the list of things to do, it "should" be in the next update ;)
In the meantime, if you want to do it yourself, you'll need to take DialogAlert that already exists in MaterialUI, duplicated it, renamed it to DialogPrompt or something and create your own script.
- First go to MaterialUI/Prefabs/Resources/Dialogs/ and duplicate the DialogAlert prefab
- Put it in the scene, and add an input field to it, save it to a new prefab (DialogPrompt)
- Duplicate the MaterialUI/Scripts/Components/Dialogs/DialogAlert.cs script, and rename it to DialogPrompt
- Add all the code needed to capture the input from the input field and callbacks etc...
But as I said, it should be in the next version ;)