title: how to put text at random position in xaringan
body: <p>I'm trying to put some text in the slides at certain position on top of other stuffs/plots, is that possible? Here is one scenario, the slide is occupied by pictures and texts, but I like to give one sentence conclusion by a different color on top of them, the text just like a stamp to the slide, it's better if I also can adjust the text orientation, just like in powerpoint or keynote, you can add text at any position and style.</p>