Sketch App and System Fonts

When I try to open a new document from a template, and specify iOS 9 UI, Sketch gives me the following warning: "Some Fonts in this Document are Missing. "The following fonts are used, but cannot be found on your system." It then lists a number of SFUI fonts, like SFUIDisplay - Semibold. How do I resolve this font issue? I'm running El Capitain and the font is not in the System Fonts folder. In fact, the SanFrancisco system font is a "hidden" font that can't be found.

Here's a full list of the fonts Sketch App is looking for.

SFUIText-Medium

SFUIDisplay-Semibold

SFUIDisplay-Regular

SFUIText-Regular

SFUIDisplay-Thin

SFUIDisplay-Light

SFUIText-Semibold

In closing, the error message says: "Opening the document will preserve the missing fonts as long as those text layers are not edited."