You can easily create footnotes in a slide using the standard Markdown syntax:

Here is some text containing a footnote.[^somesamplefootnote]

## Title 2
- Item 1
- Item 2 **bold** 
	- Sub item
	- sub item 2
		- Sub sub item
[^somesamplefootnote]: Here is the text of the footnote itself.


Foootnotes are only supported in themes (and layout) supporting them. The layout need to define the place in the slide where footnotes will be rendered.