You can download the San Francisco Font freely from the new Apple Design Resources Github page.The San Francisco font is the typeface used by Apple in the Apple Watch, iOS 9, and OS X El Capitan.
And, here is how you install those fonts for Adobe Photoshop.
Background via Wikipedia: “San Francisco is a neo-grotesque sans-serif typeface made by Apple Inc. It was first released to developers on November 18, 2014. It slightly resembles the older font Geneva, but with a few differences. It was used first as the system typeface of the Apple Watch, and later replaced Helvetica Neue as the system typeface of macOS and iOS with OS X El Capitan and iOS 9. It is also the system typeface of tvOS, starting with the 4th generation Apple TV. It is the first new typeface designed at Apple in nearly 20 years. SF Mono, the third member of the family, was introduced at WWDC 2016 and used in the conference’s website, as well as throughout the conference, on posters, signs, and marketing materials, and was first released to the public as part of Xcode 8 beta 1.“